From b533184fc353d4a2d07929b4ac424a6f1bf5a3b9 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Fri, 26 Oct 2007 18:05:40 -0400 Subject: locks: clarify posix_locks_deadlock For such a short function (with such a long comment), posix_locks_deadlock() seems to cause a lot of confusion. Attempt to make it a bit clearer: - Remove the initial posix_same_owner() check, which can never pass (since this is only called in the case that block_fl and caller_fl conflict) - Use an explicit loop (and a helper function) instead of a goto. - Rewrite the comment, attempting a clearer explanation, and removing some uninteresting historical detail. Signed-off-by: J. Bruce Fields --- fs/locks.c | 70 +++++++++++++++++++++++++++++++++++--------------------------- 1 file changed, 40 insertions(+), 30 deletions(-) (limited to 'fs') diff --git a/fs/locks.c b/fs/locks.c index 8b8388eca05e..c3eecb895acf 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -683,45 +683,55 @@ posix_test_lock(struct file *filp, struct file_lock *fl) EXPORT_SYMBOL(posix_test_lock); -/* This function tests for deadlock condition before putting a process to - * sleep. The detection scheme is no longer recursive. Recursive was neat, - * but dangerous - we risked stack corruption if the lock data was bad, or - * if the recursion was too deep for any other reason. - * - * We rely on the fact that a task can only be on one lock's wait queue - * at a time. When we find blocked_task on a wait queue we can re-search - * with blocked_task equal to that queue's owner, until either blocked_task - * isn't found, or blocked_task is found on a queue owned by my_task. - * - * Note: the above assumption may not be true when handling lock requests - * from a broken NFS client. But broken NFS clients have a lot more to - * worry about than proper deadlock detection anyway... --okir - * - * However, the failure of this assumption (also possible in the case of - * multiple tasks sharing the same open file table) also means there's no - * guarantee that the loop below will terminate. As a hack, we give up - * after a few iterations. +/* + * Deadlock detection: + * + * We attempt to detect deadlocks that are due purely to posix file + * locks. + * + * We assume that a task can be waiting for at most one lock at a time. + * So for any acquired lock, the process holding that lock may be + * waiting on at most one other lock. That lock in turns may be held by + * someone waiting for at most one other lock. Given a requested lock + * caller_fl which is about to wait for a conflicting lock block_fl, we + * follow this chain of waiters to ensure we are not about to create a + * cycle. + * + * Since we do this before we ever put a process to sleep on a lock, we + * are ensured that there is never a cycle; that is what guarantees that + * the while() loop in posix_locks_deadlock() eventually completes. + * + * Note: the above assumption may not be true when handling lock + * requests from a broken NFS client. It may also fail in the presence + * of tasks (such as posix threads) sharing the same open file table. + * + * To handle those cases, we just bail out after a few iterations. */ #define MAX_DEADLK_ITERATIONS 10 +/* Find a lock that the owner of the given block_fl is blocking on. */ +static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl) +{ + struct file_lock *fl; + + list_for_each_entry(fl, &blocked_list, fl_link) { + if (posix_same_owner(fl, block_fl)) + return fl->fl_next; + } + return NULL; +} + static int posix_locks_deadlock(struct file_lock *caller_fl, struct file_lock *block_fl) { - struct file_lock *fl; int i = 0; -next_task: - if (posix_same_owner(caller_fl, block_fl)) - return 1; - list_for_each_entry(fl, &blocked_list, fl_link) { - if (posix_same_owner(fl, block_fl)) { - if (i++ > MAX_DEADLK_ITERATIONS) - return 0; - fl = fl->fl_next; - block_fl = fl; - goto next_task; - } + while ((block_fl = what_owner_is_waiting_for(block_fl))) { + if (i++ > MAX_DEADLK_ITERATIONS) + return 0; + if (posix_same_owner(caller_fl, block_fl)) + return 1; } return 0; } -- cgit v1.2.1 From 4321e01e7dce8042758349ffa2929c723b0d4107 Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Mon, 14 Jan 2008 21:28:30 -0700 Subject: file locks: Use wait_event_interruptible_timeout() interruptible_sleep_on_locked() is just an open-coded wait_event_interruptible_timeout(), with the one difference that interruptible_sleep_on_locked() doesn't bother to check the condition on which it is waiting, depending instead on the BKL to avoid the case where it blocks after the wakeup has already been called. locks_block_on_timeout() is only used in one place, so it's actually simpler to inline it into its caller. Signed-off-by: Matthew Wilcox Signed-off-by: J. Bruce Fields --- fs/locks.c | 32 ++++---------------------------- 1 file changed, 4 insertions(+), 28 deletions(-) (limited to 'fs') diff --git a/fs/locks.c b/fs/locks.c index c3eecb895acf..faddccb6336a 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -634,33 +634,6 @@ static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *s return (locks_conflict(caller_fl, sys_fl)); } -static int interruptible_sleep_on_locked(wait_queue_head_t *fl_wait, int timeout) -{ - int result = 0; - DECLARE_WAITQUEUE(wait, current); - - __set_current_state(TASK_INTERRUPTIBLE); - add_wait_queue(fl_wait, &wait); - if (timeout == 0) - schedule(); - else - result = schedule_timeout(timeout); - if (signal_pending(current)) - result = -ERESTARTSYS; - remove_wait_queue(fl_wait, &wait); - __set_current_state(TASK_RUNNING); - return result; -} - -static int locks_block_on_timeout(struct file_lock *blocker, struct file_lock *waiter, int time) -{ - int result; - locks_insert_block(blocker, waiter); - result = interruptible_sleep_on_locked(&waiter->fl_wait, time); - __locks_delete_block(waiter); - return result; -} - void posix_test_lock(struct file *filp, struct file_lock *fl) { @@ -1266,7 +1239,10 @@ restart: if (break_time == 0) break_time++; } - error = locks_block_on_timeout(flock, new_fl, break_time); + locks_insert_block(flock, new_fl); + error = wait_event_interruptible_timeout(new_fl->fl_wait, + !new_fl->fl_next, break_time); + __locks_delete_block(new_fl); if (error >= 0) { if (error == 0) time_out_leases(inode); -- cgit v1.2.1 From ab1f16116527e42dec8aee176d673a41a881b809 Mon Sep 17 00:00:00 2001 From: Vitaliy Gusev Date: Thu, 17 Jan 2008 00:07:08 +0000 Subject: pid-namespaces-vs-locks-interaction fcntl(F_GETLK,..) can return pid of process for not current pid namespace (if process is belonged to the several namespaces). It is true also for pids in /proc/locks. So correct behavior is saving pointer to the struct pid of the process lock owner. Signed-off-by: Vitaliy Gusev Acked-by: Serge Hallyn Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: J. Bruce Fields --- fs/locks.c | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 deletions(-) (limited to 'fs') diff --git a/fs/locks.c b/fs/locks.c index faddccb6336a..49354b9c7dc1 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -125,6 +125,7 @@ #include #include #include +#include #include #include @@ -185,6 +186,7 @@ void locks_init_lock(struct file_lock *fl) fl->fl_fasync = NULL; fl->fl_owner = NULL; fl->fl_pid = 0; + fl->fl_nspid = NULL; fl->fl_file = NULL; fl->fl_flags = 0; fl->fl_type = 0; @@ -553,6 +555,8 @@ static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl) { list_add(&fl->fl_link, &file_lock_list); + fl->fl_nspid = get_pid(task_tgid(current)); + /* insert into file's list */ fl->fl_next = *pos; *pos = fl; @@ -584,6 +588,11 @@ static void locks_delete_lock(struct file_lock **thisfl_p) if (fl->fl_ops && fl->fl_ops->fl_remove) fl->fl_ops->fl_remove(fl); + if (fl->fl_nspid) { + put_pid(fl->fl_nspid); + fl->fl_nspid = NULL; + } + locks_wake_up_blocks(fl); locks_free_lock(fl); } @@ -646,14 +655,16 @@ posix_test_lock(struct file *filp, struct file_lock *fl) if (posix_locks_conflict(fl, cfl)) break; } - if (cfl) + if (cfl) { __locks_copy_lock(fl, cfl); - else + if (cfl->fl_nspid) + fl->fl_pid = pid_nr_ns(cfl->fl_nspid, + task_active_pid_ns(current)); + } else fl->fl_type = F_UNLCK; unlock_kernel(); return; } - EXPORT_SYMBOL(posix_test_lock); /* @@ -2070,6 +2081,12 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl, int id, char *pfx) { struct inode *inode = NULL; + unsigned int fl_pid; + + if (fl->fl_nspid) + fl_pid = pid_nr_ns(fl->fl_nspid, task_active_pid_ns(current)); + else + fl_pid = fl->fl_pid; if (fl->fl_file != NULL) inode = fl->fl_file->f_path.dentry->d_inode; @@ -2110,16 +2127,16 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl, } if (inode) { #ifdef WE_CAN_BREAK_LSLK_NOW - seq_printf(f, "%d %s:%ld ", fl->fl_pid, + seq_printf(f, "%d %s:%ld ", fl_pid, inode->i_sb->s_id, inode->i_ino); #else /* userspace relies on this representation of dev_t ;-( */ - seq_printf(f, "%d %02x:%02x:%ld ", fl->fl_pid, + seq_printf(f, "%d %02x:%02x:%ld ", fl_pid, MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev), inode->i_ino); #endif } else { - seq_printf(f, "%d :0 ", fl->fl_pid); + seq_printf(f, "%d :0 ", fl_pid); } if (IS_POSIX(fl)) { if (fl->fl_end == OFFSET_MAX) -- cgit v1.2.1