diff options
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/lockdep.c | 966 | ||||
| -rw-r--r-- | kernel/locking/lockdep_internals.h | 7 | ||||
| -rw-r--r-- | kernel/locking/lockdep_proc.c | 12 | ||||
| -rw-r--r-- | kernel/locking/qspinlock.c | 21 | ||||
| -rw-r--r-- | kernel/locking/qspinlock_stat.h | 21 | ||||
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 4 |
6 files changed, 857 insertions, 174 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 95932333a48b..fda370ca529c 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -45,11 +45,13 @@ #include <linux/hash.h> #include <linux/ftrace.h> #include <linux/stringify.h> +#include <linux/bitmap.h> #include <linux/bitops.h> #include <linux/gfp.h> #include <linux/random.h> #include <linux/jhash.h> #include <linux/nmi.h> +#include <linux/rcupdate.h> #include <asm/sections.h> @@ -81,6 +83,7 @@ module_param(lock_stat, int, 0644); * code to recurse back into the lockdep code... */ static arch_spinlock_t lockdep_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; +static struct task_struct *lockdep_selftest_task_struct; static int graph_lock(void) { @@ -130,13 +133,17 @@ static inline int debug_locks_off_graph_unlock(void) unsigned long nr_list_entries; static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES]; +static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES); /* * All data structures here are protected by the global debug_lock. * - * Mutex key structs only get allocated, once during bootup, and never - * get freed - this significantly simplifies the debugging code. + * nr_lock_classes is the number of elements of lock_classes[] that is + * in use. */ +#define KEYHASH_BITS (MAX_LOCKDEP_KEYS_BITS - 1) +#define KEYHASH_SIZE (1UL << KEYHASH_BITS) +static struct hlist_head lock_keys_hash[KEYHASH_SIZE]; unsigned long nr_lock_classes; #ifndef CONFIG_DEBUG_LOCKDEP static @@ -277,11 +284,42 @@ static inline void lock_release_holdtime(struct held_lock *hlock) #endif /* - * We keep a global list of all lock classes. The list only grows, - * never shrinks. The list is only accessed with the lockdep - * spinlock lock held. + * We keep a global list of all lock classes. The list is only accessed with + * the lockdep spinlock lock held. free_lock_classes is a list with free + * elements. These elements are linked together by the lock_entry member in + * struct lock_class. */ LIST_HEAD(all_lock_classes); +static LIST_HEAD(free_lock_classes); + +/** + * struct pending_free - information about data structures about to be freed + * @zapped: Head of a list with struct lock_class elements. + * @lock_chains_being_freed: Bitmap that indicates which lock_chains[] elements + * are about to be freed. + */ +struct pending_free { + struct list_head zapped; + DECLARE_BITMAP(lock_chains_being_freed, MAX_LOCKDEP_CHAINS); +}; + +/** + * struct delayed_free - data structures used for delayed freeing + * + * A data structure for delayed freeing of data structures that may be + * accessed by RCU readers at the time these were freed. + * + * @rcu_head: Used to schedule an RCU callback for freeing data structures. + * @index: Index of @pf to which freed data structures are added. + * @scheduled: Whether or not an RCU callback has been scheduled. + * @pf: Array with information about data structures about to be freed. + */ +static struct delayed_free { + struct rcu_head rcu_head; + int index; + int scheduled; + struct pending_free pf[2]; +} delayed_free; /* * The lockdep classes are in a hash-table as well, for fast lookup: @@ -331,6 +369,11 @@ void lockdep_on(void) } EXPORT_SYMBOL(lockdep_on); +void lockdep_set_selftest_task(struct task_struct *task) +{ + lockdep_selftest_task_struct = task; +} + /* * Debugging switches: */ @@ -599,7 +642,7 @@ static int very_verbose(struct lock_class *class) * Is this the address of a static object: */ #ifdef __KERNEL__ -static int static_obj(void *obj) +static int static_obj(const void *obj) { unsigned long start = (unsigned long) &_stext, end = (unsigned long) &_end, @@ -716,6 +759,17 @@ static bool assign_lock_key(struct lockdep_map *lock) { unsigned long can_addr, addr = (unsigned long)lock; +#ifdef __KERNEL__ + /* + * lockdep_free_key_range() assumes that struct lock_class_key + * objects do not overlap. Since we use the address of lock + * objects as class key for static objects, check whether the + * size of lock_class_key objects does not exceed the size of + * the smallest lock object. + */ + BUILD_BUG_ON(sizeof(struct lock_class_key) > sizeof(raw_spinlock_t)); +#endif + if (__is_kernel_percpu_address(addr, &can_addr)) lock->key = (void *)can_addr; else if (__is_module_percpu_address(addr, &can_addr)) @@ -735,6 +789,280 @@ static bool assign_lock_key(struct lockdep_map *lock) return true; } +#ifdef CONFIG_DEBUG_LOCKDEP + +/* Check whether element @e occurs in list @h */ +static bool in_list(struct list_head *e, struct list_head *h) +{ + struct list_head *f; + + list_for_each(f, h) { + if (e == f) + return true; + } + + return false; +} + +/* + * Check whether entry @e occurs in any of the locks_after or locks_before + * lists. + */ +static bool in_any_class_list(struct list_head *e) +{ + struct lock_class *class; + int i; + + for (i = 0; i < ARRAY_SIZE(lock_classes); i++) { + class = &lock_classes[i]; + if (in_list(e, &class->locks_after) || + in_list(e, &class->locks_before)) + return true; + } + return false; +} + +static bool class_lock_list_valid(struct lock_class *c, struct list_head *h) +{ + struct lock_list *e; + + list_for_each_entry(e, h, entry) { + if (e->links_to != c) { + printk(KERN_INFO "class %s: mismatch for lock entry %ld; class %s <> %s", + c->name ? : "(?)", + (unsigned long)(e - list_entries), + e->links_to && e->links_to->name ? + e->links_to->name : "(?)", + e->class && e->class->name ? e->class->name : + "(?)"); + return false; + } + } + return true; +} + +static u16 chain_hlocks[]; + +static bool check_lock_chain_key(struct lock_chain *chain) +{ +#ifdef CONFIG_PROVE_LOCKING + u64 chain_key = 0; + int i; + + for (i = chain->base; i < chain->base + chain->depth; i++) + chain_key = iterate_chain_key(chain_key, chain_hlocks[i] + 1); + /* + * The 'unsigned long long' casts avoid that a compiler warning + * is reported when building tools/lib/lockdep. + */ + if (chain->chain_key != chain_key) { + printk(KERN_INFO "chain %lld: key %#llx <> %#llx\n", + (unsigned long long)(chain - lock_chains), + (unsigned long long)chain->chain_key, + (unsigned long long)chain_key); + return false; + } +#endif + return true; +} + +static bool in_any_zapped_class_list(struct lock_class *class) +{ + struct pending_free *pf; + int i; + + for (i = 0, pf = delayed_free.pf; i < ARRAY_SIZE(delayed_free.pf); i++, pf++) { + if (in_list(&class->lock_entry, &pf->zapped)) + return true; + } + + return false; +} + +static bool __check_data_structures(void) +{ + struct lock_class *class; + struct lock_chain *chain; + struct hlist_head *head; + struct lock_list *e; + int i; + + /* Check whether all classes occur in a lock list. */ + for (i = 0; i < ARRAY_SIZE(lock_classes); i++) { + class = &lock_classes[i]; + if (!in_list(&class->lock_entry, &all_lock_classes) && + !in_list(&class->lock_entry, &free_lock_classes) && + !in_any_zapped_class_list(class)) { + printk(KERN_INFO "class %px/%s is not in any class list\n", + class, class->name ? : "(?)"); + return false; + } + } + + /* Check whether all classes have valid lock lists. */ + for (i = 0; i < ARRAY_SIZE(lock_classes); i++) { + class = &lock_classes[i]; + if (!class_lock_list_valid(class, &class->locks_before)) + return false; + if (!class_lock_list_valid(class, &class->locks_after)) + return false; + } + + /* Check the chain_key of all lock chains. */ + for (i = 0; i < ARRAY_SIZE(chainhash_table); i++) { + head = chainhash_table + i; + hlist_for_each_entry_rcu(chain, head, entry) { + if (!check_lock_chain_key(chain)) + return false; + } + } + + /* + * Check whether all list entries that are in use occur in a class + * lock list. + */ + for_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) { + e = list_entries + i; + if (!in_any_class_list(&e->entry)) { + printk(KERN_INFO "list entry %d is not in any class list; class %s <> %s\n", + (unsigned int)(e - list_entries), + e->class->name ? : "(?)", + e->links_to->name ? : "(?)"); + return false; + } + } + + /* + * Check whether all list entries that are not in use do not occur in + * a class lock list. + */ + for_each_clear_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) { + e = list_entries + i; + if (in_any_class_list(&e->entry)) { + printk(KERN_INFO "list entry %d occurs in a class list; class %s <> %s\n", + (unsigned int)(e - list_entries), + e->class && e->class->name ? e->class->name : + "(?)", + e->links_to && e->links_to->name ? + e->links_to->name : "(?)"); + return false; + } + } + + return true; +} + +int check_consistency = 0; +module_param(check_consistency, int, 0644); + +static void check_data_structures(void) +{ + static bool once = false; + + if (check_consistency && !once) { + if (!__check_data_structures()) { + once = true; + WARN_ON(once); + } + } +} + +#else /* CONFIG_DEBUG_LOCKDEP */ + +static inline void check_data_structures(void) { } + +#endif /* CONFIG_DEBUG_LOCKDEP */ + +/* + * Initialize the lock_classes[] array elements, the free_lock_classes list + * and also the delayed_free structure. + */ +static void init_data_structures_once(void) +{ + static bool initialization_happened; + int i; + + if (likely(initialization_happened)) + return; + + initialization_happened = true; + + init_rcu_head(&delayed_free.rcu_head); + INIT_LIST_HEAD(&delayed_free.pf[0].zapped); + INIT_LIST_HEAD(&delayed_free.pf[1].zapped); + + for (i = 0; i < ARRAY_SIZE(lock_classes); i++) { + list_add_tail(&lock_classes[i].lock_entry, &free_lock_classes); + INIT_LIST_HEAD(&lock_classes[i].locks_after); + INIT_LIST_HEAD(&lock_classes[i].locks_before); + } +} + +static inline struct hlist_head *keyhashentry(const struct lock_class_key *key) +{ + unsigned long hash = hash_long((uintptr_t)key, KEYHASH_BITS); + + return lock_keys_hash + hash; +} + +/* Register a dynamically allocated key. */ +void lockdep_register_key(struct lock_class_key *key) +{ + struct hlist_head *hash_head; + struct lock_class_key *k; + unsigned long flags; + + if (WARN_ON_ONCE(static_obj(key))) + return; + hash_head = keyhashentry(key); + + raw_local_irq_save(flags); + if (!graph_lock()) + goto restore_irqs; + hlist_for_each_entry_rcu(k, hash_head, hash_entry) { + if (WARN_ON_ONCE(k == key)) + goto out_unlock; + } + hlist_add_head_rcu(&key->hash_entry, hash_head); +out_unlock: + graph_unlock(); +restore_irqs: + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(lockdep_register_key); + +/* Check whether a key has been registered as a dynamic key. */ +static bool is_dynamic_key(const struct lock_class_key *key) +{ + struct hlist_head *hash_head; + struct lock_class_key *k; + bool found = false; + + if (WARN_ON_ONCE(static_obj(key))) + return false; + + /* + * If lock debugging is disabled lock_keys_hash[] may contain + * pointers to memory that has already been freed. Avoid triggering + * a use-after-free in that case by returning early. + */ + if (!debug_locks) + return true; + + hash_head = keyhashentry(key); + + rcu_read_lock(); + hlist_for_each_entry_rcu(k, hash_head, hash_entry) { + if (k == key) { + found = true; + break; + } + } + rcu_read_unlock(); + + return found; +} + /* * Register a lock's class in the hash-table, if the class is not present * yet. Otherwise we look it up. We cache the result in the lock object @@ -756,7 +1084,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) if (!lock->key) { if (!assign_lock_key(lock)) return NULL; - } else if (!static_obj(lock->key)) { + } else if (!static_obj(lock->key) && !is_dynamic_key(lock->key)) { return NULL; } @@ -775,11 +1103,12 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) goto out_unlock_set; } - /* - * Allocate a new key from the static array, and add it to - * the hash: - */ - if (nr_lock_classes >= MAX_LOCKDEP_KEYS) { + init_data_structures_once(); + + /* Allocate a new lock class and add it to the hash. */ + class = list_first_entry_or_null(&free_lock_classes, typeof(*class), + lock_entry); + if (!class) { if (!debug_locks_off_graph_unlock()) { return NULL; } @@ -788,13 +1117,13 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) dump_stack(); return NULL; } - class = lock_classes + nr_lock_classes++; + nr_lock_classes++; debug_atomic_inc(nr_unused_locks); class->key = key; class->name = lock->name; class->subclass = subclass; - INIT_LIST_HEAD(&class->locks_before); - INIT_LIST_HEAD(&class->locks_after); + WARN_ON_ONCE(!list_empty(&class->locks_before)); + WARN_ON_ONCE(!list_empty(&class->locks_after)); class->name_version = count_matching_names(class); /* * We use RCU's safe list-add method to make @@ -802,9 +1131,10 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force) */ hlist_add_head_rcu(&class->hash_entry, hash_head); /* - * Add it to the global list of classes: + * Remove the class from the free list and add it to the global list + * of classes. */ - list_add_tail(&class->lock_entry, &all_lock_classes); + list_move_tail(&class->lock_entry, &all_lock_classes); if (verbose(class)) { graph_unlock(); @@ -845,7 +1175,10 @@ out_set_class_cache: */ static struct lock_list *alloc_list_entry(void) { - if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) { + int idx = find_first_zero_bit(list_entries_in_use, + ARRAY_SIZE(list_entries)); + + if (idx >= ARRAY_SIZE(list_entries)) { if (!debug_locks_off_graph_unlock()) return NULL; @@ -853,13 +1186,16 @@ static struct lock_list *alloc_list_entry(void) dump_stack(); return NULL; } - return list_entries + nr_list_entries++; + nr_list_entries++; + __set_bit(idx, list_entries_in_use); + return list_entries + idx; } /* * Add a new dependency to the head of the list: */ -static int add_lock_to_list(struct lock_class *this, struct list_head *head, +static int add_lock_to_list(struct lock_class *this, + struct lock_class *links_to, struct list_head *head, unsigned long ip, int distance, struct stack_trace *trace) { @@ -873,6 +1209,7 @@ static int add_lock_to_list(struct lock_class *this, struct list_head *head, return 0; entry->class = this; + entry->links_to = links_to; entry->distance = distance; entry->trace = *trace; /* @@ -955,7 +1292,7 @@ static inline void mark_lock_accessed(struct lock_list *lock, unsigned long nr; nr = lock - list_entries; - WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */ + WARN_ON(nr >= ARRAY_SIZE(list_entries)); /* Out-of-bounds, input fail */ lock->parent = parent; lock->class->dep_gen_id = lockdep_dependency_gen_id; } @@ -965,7 +1302,7 @@ static inline unsigned long lock_accessed(struct lock_list *lock) unsigned long nr; nr = lock - list_entries; - WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */ + WARN_ON(nr >= ARRAY_SIZE(list_entries)); /* Out-of-bounds, input fail */ return lock->class->dep_gen_id == lockdep_dependency_gen_id; } @@ -1624,29 +1961,18 @@ static const char *state_rnames[] = { static inline const char *state_name(enum lock_usage_bit bit) { - return (bit & 1) ? state_rnames[bit >> 2] : state_names[bit >> 2]; + return (bit & LOCK_USAGE_READ_MASK) ? state_rnames[bit >> 2] : state_names[bit >> 2]; } static int exclusive_bit(int new_bit) { - /* - * USED_IN - * USED_IN_READ - * ENABLED - * ENABLED_READ - * - * bit 0 - write/read - * bit 1 - used_in/enabled - * bit 2+ state - */ - - int state = new_bit & ~3; - int dir = new_bit & 2; + int state = new_bit & LOCK_USAGE_STATE_MASK; + int dir = new_bit & LOCK_USAGE_DIR_MASK; /* * keep state, bit flip the direction and strip read. */ - return state | (dir ^ 2); + return state | (dir ^ LOCK_USAGE_DIR_MASK); } static int check_irq_usage(struct task_struct *curr, struct held_lock *prev, @@ -1842,6 +2168,24 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, struct lock_list this; int ret; + if (!hlock_class(prev)->key || !hlock_class(next)->key) { + /* + * The warning statements below may trigger a use-after-free + * of the class name. It is better to trigger a use-after free + * and to have the class name most of the time instead of not + * having the class name available. + */ + WARN_ONCE(!debug_locks_silent && !hlock_class(prev)->key, + "Detected use-after-free of lock class %px/%s\n", + hlock_class(prev), + hlock_class(prev)->name); + WARN_ONCE(!debug_locks_silent && !hlock_class(next)->key, + "Detected use-after-free of lock class %px/%s\n", + hlock_class(next), + hlock_class(next)->name); + return 2; + } + /* * Prove that the new <prev> -> <next> dependency would not * create a circular dependency in the graph. (We do this by @@ -1918,14 +2262,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, * Ok, all validations passed, add the new lock * to the previous lock's dependency list: */ - ret = add_lock_to_list(hlock_class(next), + ret = add_lock_to_list(hlock_class(next), hlock_class(prev), &hlock_class(prev)->locks_after, next->acquire_ip, distance, trace); if (!ret) return 0; - ret = add_lock_to_list(hlock_class(prev), + ret = add_lock_to_list(hlock_class(prev), hlock_class(next), &hlock_class(next)->locks_before, next->acquire_ip, distance, trace); if (!ret) @@ -2018,8 +2362,8 @@ out_bug: return 0; } -unsigned long nr_lock_chains; struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS]; +static DECLARE_BITMAP(lock_chains_in_use, MAX_LOCKDEP_CHAINS); int nr_chain_hlocks; static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS]; @@ -2153,6 +2497,33 @@ static int check_no_collision(struct task_struct *curr, } /* + * Given an index that is >= -1, return the index of the next lock chain. + * Return -2 if there is no next lock chain. + */ +long lockdep_next_lockchain(long i) +{ + i = find_next_bit(lock_chains_in_use, ARRAY_SIZE(lock_chains), i + 1); + return i < ARRAY_SIZE(lock_chains) ? i : -2; +} + +unsigned long lock_chain_count(void) +{ + return bitmap_weight(lock_chains_in_use, ARRAY_SIZE(lock_chains)); +} + +/* Must be called with the graph lock held. */ +static struct lock_chain *alloc_lock_chain(void) +{ + int idx = find_first_zero_bit(lock_chains_in_use, + ARRAY_SIZE(lock_chains)); + + if (unlikely(idx >= ARRAY_SIZE(lock_chains))) + return NULL; + __set_bit(idx, lock_chains_in_use); + return lock_chains + idx; +} + +/* * Adds a dependency chain into chain hashtable. And must be called with * graph_lock held. * @@ -2169,19 +2540,15 @@ static inline int add_chain_cache(struct task_struct *curr, int i, j; /* - * Allocate a new chain entry from the static array, and add - * it to the hash: - */ - - /* - * We might need to take the graph lock, ensure we've got IRQs + * The caller must hold the graph lock, ensure we've got IRQs * disabled to make this an IRQ-safe lock.. for recursion reasons * lockdep won't complain about its own locking errors. */ if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) return 0; - if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) { + chain = alloc_lock_chain(); + if (!chain) { if (!debug_locks_off_graph_unlock()) return 0; @@ -2189,7 +2556,6 @@ static inline int add_chain_cache(struct task_struct *curr, dump_stack(); return 0; } - chain = lock_chains + nr_lock_chains++; chain->chain_key = chain_key; chain->irq_context = hlock->irq_context; i = get_first_held_lock(curr, hlock); @@ -2206,16 +2572,8 @@ static inline int add_chain_cache(struct task_struct *curr, chain_hlocks[chain->base + j] = lock_id; } chain_hlocks[chain->base + j] = class - lock_classes; - } - - if (nr_chain_hlocks < MAX_LOCKDEP_CHAIN_HLOCKS) nr_chain_hlocks += chain->depth; - -#ifdef CONFIG_DEBUG_LOCKDEP - /* - * Important for check_no_collision(). - */ - if (unlikely(nr_chain_hlocks > MAX_LOCKDEP_CHAIN_HLOCKS)) { + } else { if (!debug_locks_off_graph_unlock()) return 0; @@ -2223,7 +2581,6 @@ static inline int add_chain_cache(struct task_struct *curr, dump_stack(); return 0; } -#endif hlist_add_head_rcu(&chain->entry, hash_head); debug_atomic_inc(chain_lookup_misses); @@ -2233,19 +2590,16 @@ static inline int add_chain_cache(struct task_struct *curr, } /* - * Look up a dependency chain. + * Look up a dependency chain. Must be called with either the graph lock or + * the RCU read lock held. */ static inline struct lock_chain *lookup_chain_cache(u64 chain_key) { struct hlist_head *hash_head = chainhashentry(chain_key); struct lock_chain *chain; - /* - * We can walk it lock-free, because entries only get added - * to the hash: - */ hlist_for_each_entry_rcu(chain, hash_head, entry) { - if (chain->chain_key == chain_key) { + if (READ_ONCE(chain->chain_key) == chain_key) { debug_atomic_inc(chain_lookup_hits); return chain; } @@ -2662,8 +3016,8 @@ mark_lock_irq(struct task_struct *curr, struct held_lock *this, enum lock_usage_bit new_bit) { int excl_bit = exclusive_bit(new_bit); - int read = new_bit & 1; - int dir = new_bit & 2; + int read = new_bit & LOCK_USAGE_READ_MASK; + int dir = new_bit & LOCK_USAGE_DIR_MASK; /* * mark USED_IN has to look forwards -- to ensure no dependency @@ -2687,19 +3041,19 @@ mark_lock_irq(struct task_struct *curr, struct held_lock *this, * states. */ if ((!read || !dir || STRICT_READ_CHECKS) && - !usage(curr, this, excl_bit, state_name(new_bit & ~1))) + !usage(curr, this, excl_bit, state_name(new_bit & ~LOCK_USAGE_READ_MASK))) return 0; /* * Check for read in write conflicts */ if (!read) { - if (!valid_state(curr, this, new_bit, excl_bit + 1)) + if (!valid_state(curr, this, new_bit, excl_bit + LOCK_USAGE_READ_MASK)) return 0; if (STRICT_READ_CHECKS && - !usage(curr, this, excl_bit + 1, - state_name(new_bit + 1))) + !usage(curr, this, excl_bit + LOCK_USAGE_READ_MASK, + state_name(new_bit + LOCK_USAGE_READ_MASK))) return 0; } @@ -2709,35 +3063,28 @@ mark_lock_irq(struct task_struct *curr, struct held_lock *this, return 1; } -enum mark_type { -#define LOCKDEP_STATE(__STATE) __STATE, -#include "lockdep_states.h" -#undef LOCKDEP_STATE -}; - /* * Mark all held locks with a usage bit: */ static int -mark_held_locks(struct task_struct *curr, enum mark_type mark) +mark_held_locks(struct task_struct *curr, enum lock_usage_bit base_bit) { - enum lock_usage_bit usage_bit; struct held_lock *hlock; int i; for (i = 0; i < curr->lockdep_depth; i++) { + enum lock_usage_bit hlock_bit = base_bit; hlock = curr->held_locks + i; - usage_bit = 2 + (mark << 2); /* ENABLED */ if (hlock->read) - usage_bit += 1; /* READ */ + hlock_bit += LOCK_USAGE_READ_MASK; - BUG_ON(usage_bit >= LOCK_USAGE_STATES); + BUG_ON(hlock_bit >= LOCK_USAGE_STATES); if (!hlock->check) continue; - if (!mark_lock(curr, hlock, usage_bit)) + if (!mark_lock(curr, hlock, hlock_bit)) return 0; } @@ -2758,7 +3105,7 @@ static void __trace_hardirqs_on_caller(unsigned long ip) * We are going to turn hardirqs on, so set the * usage bit for all held locks: */ - if (!mark_held_locks(curr, HARDIRQ)) + if (!mark_held_locks(curr, LOCK_ENABLED_HARDIRQ)) return; /* * If we have softirqs enabled, then set the usage @@ -2766,7 +3113,7 @@ static void __trace_hardirqs_on_caller(unsigned long ip) * this bit from being set before) */ if (curr->softirqs_enabled) - if (!mark_held_locks(curr, SOFTIRQ)) + if (!mark_held_locks(curr, LOCK_ENABLED_SOFTIRQ)) return; curr->hardirq_enable_ip = ip; @@ -2880,7 +3227,7 @@ void trace_softirqs_on(unsigned long ip) * enabled too: */ if (curr->hardirqs_enabled) - mark_held_locks(curr, SOFTIRQ); + mark_held_locks(curr, LOCK_ENABLED_SOFTIRQ); current->lockdep_recursion = 0; } @@ -3119,13 +3466,12 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name, if (DEBUG_LOCKS_WARN_ON(!key)) return; /* - * Sanity check, the lock-class key must be persistent: + * Sanity check, the lock-class key must either have been allocated + * statically or must have been registered as a dynamic key. */ - if (!static_obj(key)) { - printk("BUG: key %px not in .data!\n", key); - /* - * What it says above ^^^^^, I suggest you read it. - */ + if (!static_obj(key) && !is_dynamic_key(key)) { + if (debug_locks) + printk(KERN_ERR "BUG: key %px has not been registered!\n", key); DEBUG_LOCKS_WARN_ON(1); return; } @@ -3335,6 +3681,11 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, if (nest_lock && !__lock_is_held(nest_lock, -1)) return print_lock_nested_lock_not_held(curr, hlock, ip); + if (!debug_locks_silent) { + WARN_ON_ONCE(depth && !hlock_class(hlock - 1)->key); + WARN_ON_ONCE(!hlock_class(hlock)->key); + } + if (!validate_chain(curr, lock, hlock, chain_head, chain_key)) return 0; @@ -3497,6 +3848,9 @@ __lock_set_class(struct lockdep_map *lock, const char *name, unsigned int depth; int i; + if (unlikely(!debug_locks)) + return 0; + depth = curr->lockdep_depth; /* * This function is about (re)setting the class of a held lock, @@ -3535,6 +3889,9 @@ static int __lock_downgrade(struct lockdep_map *lock, unsigned long ip) unsigned int depth; int i; + if (unlikely(!debug_locks)) + return 0; + depth = curr->lockdep_depth; /* * This function is about (re)setting the class of a held lock, @@ -4123,29 +4480,131 @@ void lockdep_reset(void) raw_local_irq_restore(flags); } +/* Remove a class from a lock chain. Must be called with the graph lock held. */ +static void remove_class_from_lock_chain(struct pending_free *pf, + struct lock_chain *chain, + struct lock_class *class) +{ +#ifdef CONFIG_PROVE_LOCKING + struct lock_chain *new_chain; + u64 chain_key; + int i; + + for (i = chain->base; i < chain->base + chain->depth; i++) { + if (chain_hlocks[i] != class - lock_classes) + continue; + /* The code below leaks one chain_hlock[] entry. */ + if (--chain->depth > 0) { + memmove(&chain_hlocks[i], &chain_hlocks[i + 1], + (chain->base + chain->depth - i) * + sizeof(chain_hlocks[0])); + } + /* + * Each lock class occurs at most once in a lock chain so once + * we found a match we can break out of this loop. + */ + goto recalc; + } + /* Since the chain has not been modified, return. */ + return; + +recalc: + chain_key = 0; + for (i = chain->base; i < chain->base + chain->depth; i++) + chain_key = iterate_chain_key(chain_key, chain_hlocks[i] + 1); + if (chain->depth && chain->chain_key == chain_key) + return; + /* Overwrite the chain key for concurrent RCU readers. */ + WRITE_ONCE(chain->chain_key, chain_key); + /* + * Note: calling hlist_del_rcu() from inside a + * hlist_for_each_entry_rcu() loop is safe. + */ + hlist_del_rcu(&chain->entry); + __set_bit(chain - lock_chains, pf->lock_chains_being_freed); + if (chain->depth == 0) + return; + /* + * If the modified lock chain matches an existing lock chain, drop + * the modified lock chain. + */ + if (lookup_chain_cache(chain_key)) + return; + new_chain = alloc_lock_chain(); + if (WARN_ON_ONCE(!new_chain)) { + debug_locks_off(); + return; + } + *new_chain = *chain; + hlist_add_head_rcu(&new_chain->entry, chainhashentry(chain_key)); +#endif +} + +/* Must be called with the graph lock held. */ +static void remove_class_from_lock_chains(struct pending_free *pf, + struct lock_class *class) +{ + struct lock_chain *chain; + struct hlist_head *head; + int i; + + for (i = 0; i < ARRAY_SIZE(chainhash_table); i++) { + head = chainhash_table + i; + hlist_for_each_entry_rcu(chain, head, entry) { + remove_class_from_lock_chain(pf, chain, class); + } + } +} + /* * Remove all references to a lock class. The caller must hold the graph lock. */ -static void zap_class(struct lock_class *class) +static void zap_class(struct pending_free *pf, struct lock_class *class) { + struct lock_list *entry; int i; + WARN_ON_ONCE(!class->key); + /* * Remove all dependencies this lock is * involved in: */ - for (i = 0; i < nr_list_entries; i++) { - if (list_entries[i].class == class) - list_del_rcu(&list_entries[i].entry); + for_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) { + entry = list_entries + i; + if (entry->class != class && entry->links_to != class) + continue; + __clear_bit(i, list_entries_in_use); + nr_list_entries--; + list_del_rcu(&entry->entry); + } + if (list_empty(&class->locks_after) && + list_empty(&class->locks_before)) { + list_move_tail(&class->lock_entry, &pf->zapped); + hlist_del_rcu(&class->hash_entry); + WRITE_ONCE(class->key, NULL); + WRITE_ONCE(class->name, NULL); + nr_lock_classes--; + } else { + WARN_ONCE(true, "%s() failed for class %s\n", __func__, + class->name); } - /* - * Unhash the class and remove it from the all_lock_classes list: - */ - hlist_del_rcu(&class->hash_entry); - list_del(&class->lock_entry); - RCU_INIT_POINTER(class->key, NULL); - RCU_INIT_POINTER(class->name, NULL); + remove_class_from_lock_chains(pf, class); +} + +static void reinit_class(struct lock_class *class) +{ + void *const p = class; + const unsigned int offset = offsetof(struct lock_class, key); + + WARN_ON_ONCE(!class->lock_entry.next); + WARN_ON_ONCE(!list_empty(&class->locks_after)); + WARN_ON_ONCE(!list_empty(&class->locks_before)); + memset(p + offset, 0, sizeof(*class) - offset); + WARN_ON_ONCE(!class->lock_entry.next); + WARN_ON_ONCE(!list_empty(&class->locks_after)); + WARN_ON_ONCE(!list_empty(&class->locks_before)); } static inline int within(const void *addr, void *start, unsigned long size) @@ -4153,55 +4612,175 @@ static inline int within(const void *addr, void *start, unsigned long size) return addr >= start && addr < start + size; } +static bool inside_selftest(void) +{ + return current == lockdep_selftest_task_struct; +} + +/* The caller must hold the graph lock. */ +static struct pending_free *get_pending_free(void) +{ + return delayed_free.pf + delayed_free.index; +} + +static void free_zapped_rcu(struct rcu_head *cb); + /* - * Used in module.c to remove lock classes from memory that is going to be - * freed; and possibly re-used by other modules. - * - * We will have had one sync_sched() before getting here, so we're guaranteed - * nobody will look up these exact classes -- they're properly dead but still - * allocated. + * Schedule an RCU callback if no RCU callback is pending. Must be called with + * the graph lock held. */ -void lockdep_free_key_range(void *start, unsigned long size) +static void call_rcu_zapped(struct pending_free *pf) +{ + WARN_ON_ONCE(inside_selftest()); + + if (list_empty(&pf->zapped)) + return; + + if (delayed_free.scheduled) + return; + + delayed_free.scheduled = true; + + WARN_ON_ONCE(delayed_free.pf + delayed_free.index != pf); + delayed_free.index ^= 1; + + call_rcu(&delayed_free.rcu_head, free_zapped_rcu); +} + +/* The caller must hold the graph lock. May be called from RCU context. */ +static void __free_zapped_classes(struct pending_free *pf) { struct lock_class *class; - struct hlist_head *head; + + check_data_structures(); + + list_for_each_entry(class, &pf->zapped, lock_entry) + reinit_class(class); + + list_splice_init(&pf->zapped, &free_lock_classes); + +#ifdef CONFIG_PROVE_LOCKING + bitmap_andnot(lock_chains_in_use, lock_chains_in_use, + pf->lock_chains_being_freed, ARRAY_SIZE(lock_chains)); + bitmap_clear(pf->lock_chains_being_freed, 0, ARRAY_SIZE(lock_chains)); +#endif +} + +static void free_zapped_rcu(struct rcu_head *ch) +{ + struct pending_free *pf; unsigned long flags; - int i; - int locked; + + if (WARN_ON_ONCE(ch != &delayed_free.rcu_head)) + return; raw_local_irq_save(flags); - locked = graph_lock(); + if (!graph_lock()) + goto out_irq; + + /* closed head */ + pf = delayed_free.pf + (delayed_free.index ^ 1); + __free_zapped_classes(pf); + delayed_free.scheduled = false; /* - * Unhash all classes that were created by this module: + * If there's anything on the open list, close and start a new callback. */ + call_rcu_zapped(delayed_free.pf + delayed_free.index); + + graph_unlock(); +out_irq: + raw_local_irq_restore(flags); +} + +/* + * Remove all lock classes from the class hash table and from the + * all_lock_classes list whose key or name is in the address range [start, + * start + size). Move these lock classes to the zapped_classes list. Must + * be called with the graph lock held. + */ +static void __lockdep_free_key_range(struct pending_free *pf, void *start, + unsigned long size) +{ + struct lock_class *class; + struct hlist_head *head; + int i; + + /* Unhash all classes that were created by a module. */ for (i = 0; i < CLASSHASH_SIZE; i++) { head = classhash_table + i; hlist_for_each_entry_rcu(class, head, hash_entry) { - if (within(class->key, start, size)) - zap_class(class); - else if (within(class->name, start, size)) - zap_class(class); + if (!within(class->key, start, size) && + !within(class->name, start, size)) + continue; + zap_class(pf, class); } } +} - if (locked) - graph_unlock(); +/* + * Used in module.c to remove lock classes from memory that is going to be + * freed; and possibly re-used by other modules. + * + * We will have had one synchronize_rcu() before getting here, so we're + * guaranteed nobody will look up these exact classes -- they're properly dead + * but still allocated. + */ +static void lockdep_free_key_range_reg(void *start, unsigned long size) +{ + struct pending_free *pf; + unsigned long flags; + int locked; + + init_data_structures_once(); + + raw_local_irq_save(flags); + locked = graph_lock(); + if (!locked) + goto out_irq; + + pf = get_pending_free(); + __lockdep_free_key_range(pf, start, size); + call_rcu_zapped(pf); + + graph_unlock(); +out_irq: raw_local_irq_restore(flags); /* * Wait for any possible iterators from look_up_lock_class() to pass * before continuing to free the memory they refer to. - * - * sync_sched() is sufficient because the read-side is IRQ disable. */ synchronize_rcu(); +} - /* - * XXX at this point we could return the resources to the pool; - * instead we leak them. We would need to change to bitmap allocators - * instead of the linear allocators we have now. - */ +/* + * Free all lockdep keys in the range [start, start+size). Does not sleep. + * Ignores debug_locks. Must only be used by the lockdep selftests. + */ +static void lockdep_free_key_range_imm(void *start, unsigned long size) +{ + struct pending_free *pf = delayed_free.pf; + unsigned long flags; + + init_data_structures_once(); + + raw_local_irq_save(flags); + arch_spin_lock(&lockdep_lock); + __lockdep_free_key_range(pf, start, size); + __free_zapped_classes(pf); + arch_spin_unlock(&lockdep_lock); + raw_local_irq_restore(flags); +} + +void lockdep_free_key_range(void *start, unsigned long size) +{ + init_data_structures_once(); + + if (inside_selftest()) + lockdep_free_key_range_imm(start, size); + else + lockdep_free_key_range_reg(start, size); } /* @@ -4226,14 +4805,12 @@ static bool lock_class_cache_is_registered(struct lockdep_map *lock) return false; } -void lockdep_reset_lock(struct lockdep_map *lock) +/* The caller must hold the graph lock. Does not sleep. */ +static void __lockdep_reset_lock(struct pending_free *pf, + struct lockdep_map *lock) { struct lock_class *class; - unsigned long flags; - int j, locked; - - raw_local_irq_save(flags); - locked = graph_lock(); + int j; /* * Remove all classes this lock might have: @@ -4244,27 +4821,104 @@ void lockdep_reset_lock(struct lockdep_map *lock) */ class = look_up_lock_class(lock, j); if (class) - zap_class(class); + zap_class(pf, class); } /* * Debug check: in the end all mapped classes should * be gone. */ - if (unlikely(lock_class_cache_is_registered(lock))) { - if (debug_locks_off_graph_unlock()) { - /* - * We all just reset everything, how did it match? - */ - WARN_ON(1); + if (WARN_ON_ONCE(lock_class_cache_is_registered(lock))) + debug_locks_off(); +} + +/* + * Remove all information lockdep has about a lock if debug_locks == 1. Free + * released data structures from RCU context. + */ +static void lockdep_reset_lock_reg(struct lockdep_map *lock) +{ + struct pending_free *pf; + unsigned long flags; + int locked; + + raw_local_irq_save(flags); + locked = graph_lock(); + if (!locked) + goto out_irq; + + pf = get_pending_free(); + __lockdep_reset_lock(pf, lock); + call_rcu_zapped(pf); + + graph_unlock(); +out_irq: + raw_local_irq_restore(flags); +} + +/* + * Reset a lock. Does not sleep. Ignores debug_locks. Must only be used by the + * lockdep selftests. + */ +static void lockdep_reset_lock_imm(struct lockdep_map *lock) +{ + struct pending_free *pf = delayed_free.pf; + unsigned long flags; + + raw_local_irq_save(flags); + arch_spin_lock(&lockdep_lock); + __lockdep_reset_lock(pf, lock); + __free_zapped_classes(pf); + arch_spin_unlock(&lockdep_lock); + raw_local_irq_restore(flags); +} + +void lockdep_reset_lock(struct lockdep_map *lock) +{ + init_data_structures_once(); + + if (inside_selftest()) + lockdep_reset_lock_imm(lock); + else + lockdep_reset_lock_reg(lock); +} + +/* Unregister a dynamically allocated key. */ +void lockdep_unregister_key(struct lock_class_key *key) +{ + struct hlist_head *hash_head = keyhashentry(key); + struct lock_class_key *k; + struct pending_free *pf; + unsigned long flags; + bool found = false; + + might_sleep(); + + if (WARN_ON_ONCE(static_obj(key))) + return; + + raw_local_irq_save(flags); + if (!graph_lock()) + goto out_irq; + + pf = get_pending_free(); + hlist_for_each_entry_rcu(k, hash_head, hash_entry) { + if (k == key) { + hlist_del_rcu(&k->hash_entry); + found = true; + break; } - goto out_restore; } - if (locked) - graph_unlock(); - -out_restore: + WARN_ON_ONCE(!found); + __lockdep_free_key_range(pf, key, 1); + call_rcu_zapped(pf); + graph_unlock(); +out_irq: raw_local_irq_restore(flags); + + /* Wait until is_dynamic_key() has finished accessing k->hash_entry. */ + synchronize_rcu(); } +EXPORT_SYMBOL_GPL(lockdep_unregister_key); void __init lockdep_init(void) { @@ -4278,20 +4932,24 @@ void __init lockdep_init(void) printk("... MAX_LOCKDEP_CHAINS: %lu\n", MAX_LOCKDEP_CHAINS); printk("... CHAINHASH_SIZE: %lu\n", CHAINHASH_SIZE); - printk(" memory used by lock dependency info: %lu kB\n", - (sizeof(struct lock_class) * MAX_LOCKDEP_KEYS + - sizeof(struct list_head) * CLASSHASH_SIZE + - sizeof(struct lock_list) * MAX_LOCKDEP_ENTRIES + - sizeof(struct lock_chain) * MAX_LOCKDEP_CHAINS + - sizeof(struct list_head) * CHAINHASH_SIZE + printk(" memory used by lock dependency info: %zu kB\n", + (sizeof(lock_classes) + + sizeof(classhash_table) + + sizeof(list_entries) + + sizeof(list_entries_in_use) + + sizeof(chainhash_table) + + sizeof(delayed_free) #ifdef CONFIG_PROVE_LOCKING - + sizeof(struct circular_queue) + + sizeof(lock_cq) + + sizeof(lock_chains) + + sizeof(lock_chains_in_use) + + sizeof(chain_hlocks) #endif ) / 1024 ); - printk(" per task-struct memory footprint: %lu bytes\n", - sizeof(struct held_lock) * MAX_LOCK_DEPTH); + printk(" per task-struct memory footprint: %zu bytes\n", + sizeof(((struct task_struct *)NULL)->held_locks)); } static void diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h index 88c847a41c8a..d4c197425f68 100644 --- a/kernel/locking/lockdep_internals.h +++ b/kernel/locking/lockdep_internals.h @@ -22,6 +22,10 @@ enum lock_usage_bit { LOCK_USAGE_STATES }; +#define LOCK_USAGE_READ_MASK 1 +#define LOCK_USAGE_DIR_MASK 2 +#define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK)) + /* * Usage-state bitmasks: */ @@ -96,7 +100,8 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i); extern unsigned long nr_lock_classes; extern unsigned long nr_list_entries; -extern unsigned long nr_lock_chains; +long lockdep_next_lockchain(long i); +unsigned long lock_chain_count(void); extern int nr_chain_hlocks; extern unsigned long nr_stack_trace_entries; diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c index 3d31f9b0059e..9c49ec645d8b 100644 --- a/kernel/locking/lockdep_proc.c +++ b/kernel/locking/lockdep_proc.c @@ -104,18 +104,18 @@ static const struct seq_operations lockdep_ops = { #ifdef CONFIG_PROVE_LOCKING static void *lc_start(struct seq_file *m, loff_t *pos) { + if (*pos < 0) + return NULL; + if (*pos == 0) return SEQ_START_TOKEN; - if (*pos - 1 < nr_lock_chains) - return lock_chains + (*pos - 1); - - return NULL; + return lock_chains + (*pos - 1); } static void *lc_next(struct seq_file *m, void *v, loff_t *pos) { - (*pos)++; + *pos = lockdep_next_lockchain(*pos - 1) + 1; return lc_start(m, pos); } @@ -268,7 +268,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v) #ifdef CONFIG_PROVE_LOCKING seq_printf(m, " dependency chains: %11lu [max: %lu]\n", - nr_lock_chains, MAX_LOCKDEP_CHAINS); + lock_chain_count(), MAX_LOCKDEP_CHAINS); seq_printf(m, " dependency chain hlocks: %11d [max: %lu]\n", nr_chain_hlocks, MAX_LOCKDEP_CHAIN_HLOCKS); #endif diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 8a8c3c208c5e..5e9247dc2515 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -124,9 +124,6 @@ static inline __pure u32 encode_tail(int cpu, int idx) { u32 tail; -#ifdef CONFIG_DEBUG_SPINLOCK - BUG_ON(idx > 3); -#endif tail = (cpu + 1) << _Q_TAIL_CPU_OFFSET; tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */ @@ -412,12 +409,28 @@ pv_queue: idx = node->count++; tail = encode_tail(smp_processor_id(), idx); + /* + * 4 nodes are allocated based on the assumption that there will + * not be nested NMIs taking spinlocks. That may not be true in + * some architectures even though the chance of needing more than + * 4 nodes will still be extremely unlikely. When that happens, + * we fall back to spinning on the lock directly without using + * any MCS node. This is not the most elegant solution, but is + * simple enough. + */ + if (unlikely(idx >= MAX_NODES)) { + qstat_inc(qstat_lock_no_node, true); + while (!queued_spin_trylock(lock)) + cpu_relax(); + goto release; + } + node = grab_mcs_node(node, idx); /* * Keep counts of non-zero index values: */ - qstat_inc(qstat_lock_idx1 + idx - 1, idx); + qstat_inc(qstat_lock_use_node2 + idx - 1, idx); /* * Ensure that we increment the head node->count before initialising diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h index 42d3d8dc8f49..d73f85388d5c 100644 --- a/kernel/locking/qspinlock_stat.h +++ b/kernel/locking/qspinlock_stat.h @@ -30,6 +30,13 @@ * pv_wait_node - # of vCPU wait's at a non-head queue node * lock_pending - # of locking operations via pending code * lock_slowpath - # of locking operations via MCS lock queue + * lock_use_node2 - # of locking operations that use 2nd per-CPU node + * lock_use_node3 - # of locking operations that use 3rd per-CPU node + * lock_use_node4 - # of locking operations that use 4th per-CPU node + * lock_no_node - # of locking operations without using per-CPU node + * + * Subtracting lock_use_node[234] from lock_slowpath will give you + * lock_use_node1. * * Writing to the "reset_counters" file will reset all the above counter * values. @@ -55,9 +62,10 @@ enum qlock_stats { qstat_pv_wait_node, qstat_lock_pending, qstat_lock_slowpath, - qstat_lock_idx1, - qstat_lock_idx2, - qstat_lock_idx3, + qstat_lock_use_node2, + qstat_lock_use_node3, + qstat_lock_use_node4, + qstat_lock_no_node, qstat_num, /* Total number of statistical counters */ qstat_reset_cnts = qstat_num, }; @@ -85,9 +93,10 @@ static const char * const qstat_names[qstat_num + 1] = { [qstat_pv_wait_node] = "pv_wait_node", [qstat_lock_pending] = "lock_pending", [qstat_lock_slowpath] = "lock_slowpath", - [qstat_lock_idx1] = "lock_index1", - [qstat_lock_idx2] = "lock_index2", - [qstat_lock_idx3] = "lock_index3", + [qstat_lock_use_node2] = "lock_use_node2", + [qstat_lock_use_node3] = "lock_use_node3", + [qstat_lock_use_node4] = "lock_use_node4", + [qstat_lock_no_node] = "lock_no_node", [qstat_reset_cnts] = "reset_counters", }; diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 50d9af615dc4..fbe96341beee 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -211,9 +211,7 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem, * Ensure issuing the wakeup (either by us or someone else) * after setting the reader waiter to nil. */ - wake_q_add(wake_q, tsk); - /* wake_q_add() already take the task ref */ - put_task_struct(tsk); + wake_q_add_safe(wake_q, tsk); } adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment; |
