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author | David Brown <davidb@codeaurora.org> | 2011-03-16 22:13:16 -0700 |
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committer | David Brown <davidb@codeaurora.org> | 2011-03-16 22:13:16 -0700 |
commit | 92c260f755c42337c550d8ac1f8ccd1b32bffb20 (patch) | |
tree | 6d04fefc1adeecabfb2b00c201e0db78fa2b5529 /fs/eventpoll.c | |
parent | 8e76a80960bf06c245160a484d5a363ca6b520bb (diff) | |
parent | 05e34754518b6a90d5c392790c032575fab12d66 (diff) | |
download | blackbird-obmc-linux-92c260f755c42337c550d8ac1f8ccd1b32bffb20.tar.gz blackbird-obmc-linux-92c260f755c42337c550d8ac1f8ccd1b32bffb20.zip |
Merge remote branch 'rmk/for-linus' into for-linus
* rmk/for-linus: (1557 commits)
ARM: 6806/1: irq: introduce entry and exit functions for chained handlers
ARM: 6781/1: Thumb-2: Work around buggy Thumb-2 short branch relocations in gas
ARM: 6747/1: P2V: Thumb2 support
ARM: 6798/1: aout-core: zero thread debug registers in a.out core dump
ARM: 6796/1: Footbridge: Fix I/O mappings for NOMMU mode
ARM: 6784/1: errata: no automatic Store Buffer drain on Cortex-A9
ARM: 6772/1: errata: possible fault MMU translations following an ASID switch
ARM: 6776/1: mach-ux500: activate fix for errata 753970
ARM: 6794/1: SPEAr: Append UL to device address macros.
ARM: 6793/1: SPEAr: Remove unused *_SIZE macros from spear*.h files
ARM: 6792/1: SPEAr: Replace SIZE macro's with SZ_4K macros
ARM: 6791/1: SPEAr3xx: Declare device structures after shirq code
ARM: 6790/1: SPEAr: Clock Framework: Rename usbd clock and align apb_clk entry
ARM: 6789/1: SPEAr3xx: Rename sdio to sdhci
ARM: 6788/1: SPEAr: Include mach/hardware.h instead of mach/spear.h
ARM: 6787/1: SPEAr: Reorder #includes in .h & .c files.
ARM: 6681/1: SPEAr: add debugfs support to clk API
ARM: 6703/1: SPEAr: update clk API support
ARM: 6679/1: SPEAr: make clk API functions more generic
ARM: 6737/1: SPEAr: formalized timer support
...
Conflicts:
arch/arm/mach-msm/board-msm7x27.c
arch/arm/mach-msm/board-msm7x30.c
arch/arm/mach-msm/board-qsd8x50.c
arch/arm/mach-msm/board-sapphire.c
arch/arm/mach-msm/include/mach/memory.h
Diffstat (limited to 'fs/eventpoll.c')
-rw-r--r-- | fs/eventpoll.c | 111 |
1 files changed, 108 insertions, 3 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index cc8a9b7d6064..4a09af9e9a63 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -63,6 +63,13 @@ * cleanup path and it is also acquired by eventpoll_release_file() * if a file has been pushed inside an epoll set and it is then * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL). + * It is also acquired when inserting an epoll fd onto another epoll + * fd. We do this so that we walk the epoll tree and ensure that this + * insertion does not create a cycle of epoll file descriptors, which + * could lead to deadlock. We need a global mutex to prevent two + * simultaneous inserts (A into B and B into A) from racing and + * constructing a cycle without either insert observing that it is + * going to. * It is possible to drop the "ep->mtx" and to use the global * mutex "epmutex" (together with "ep->lock") to have it working, * but having "ep->mtx" will make the interface more scalable. @@ -224,6 +231,9 @@ static long max_user_watches __read_mostly; */ static DEFINE_MUTEX(epmutex); +/* Used to check for epoll file descriptor inclusion loops */ +static struct nested_calls poll_loop_ncalls; + /* Used for safe wake up implementation */ static struct nested_calls poll_safewake_ncalls; @@ -1114,6 +1124,17 @@ static int ep_send_events(struct eventpoll *ep, return ep_scan_ready_list(ep, ep_send_events_proc, &esed); } +static inline struct timespec ep_set_mstimeout(long ms) +{ + struct timespec now, ts = { + .tv_sec = ms / MSEC_PER_SEC, + .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC), + }; + + ktime_get_ts(&now); + return timespec_add_safe(now, ts); +} + static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, long timeout) { @@ -1121,12 +1142,11 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, unsigned long flags; long slack; wait_queue_t wait; - struct timespec end_time; ktime_t expires, *to = NULL; if (timeout > 0) { - ktime_get_ts(&end_time); - timespec_add_ns(&end_time, (u64)timeout * NSEC_PER_MSEC); + struct timespec end_time = ep_set_mstimeout(timeout); + slack = select_estimate_accuracy(&end_time); to = &expires; *to = timespec_to_ktime(end_time); @@ -1188,6 +1208,62 @@ retry: return res; } +/** + * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested() + * API, to verify that adding an epoll file inside another + * epoll structure, does not violate the constraints, in + * terms of closed loops, or too deep chains (which can + * result in excessive stack usage). + * + * @priv: Pointer to the epoll file to be currently checked. + * @cookie: Original cookie for this call. This is the top-of-the-chain epoll + * data structure pointer. + * @call_nests: Current dept of the @ep_call_nested() call stack. + * + * Returns: Returns zero if adding the epoll @file inside current epoll + * structure @ep does not violate the constraints, or -1 otherwise. + */ +static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) +{ + int error = 0; + struct file *file = priv; + struct eventpoll *ep = file->private_data; + struct rb_node *rbp; + struct epitem *epi; + + mutex_lock(&ep->mtx); + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (unlikely(is_file_epoll(epi->ffd.file))) { + error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS, + ep_loop_check_proc, epi->ffd.file, + epi->ffd.file->private_data, current); + if (error != 0) + break; + } + } + mutex_unlock(&ep->mtx); + + return error; +} + +/** + * ep_loop_check - Performs a check to verify that adding an epoll file (@file) + * another epoll file (represented by @ep) does not create + * closed loops or too deep chains. + * + * @ep: Pointer to the epoll private data structure. + * @file: Pointer to the epoll file to be checked. + * + * Returns: Returns zero if adding the epoll @file inside current epoll + * structure @ep does not violate the constraints, or -1 otherwise. + */ +static int ep_loop_check(struct eventpoll *ep, struct file *file) +{ + return ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS, + ep_loop_check_proc, file, ep, current); +} + /* * Open an eventpoll file descriptor. */ @@ -1236,6 +1312,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, struct epoll_event __user *, event) { int error; + int did_lock_epmutex = 0; struct file *file, *tfile; struct eventpoll *ep; struct epitem *epi; @@ -1277,6 +1354,25 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, */ ep = file->private_data; + /* + * When we insert an epoll file descriptor, inside another epoll file + * descriptor, there is the change of creating closed loops, which are + * better be handled here, than in more critical paths. + * + * We hold epmutex across the loop check and the insert in this case, in + * order to prevent two separate inserts from racing and each doing the + * insert "at the same time" such that ep_loop_check passes on both + * before either one does the insert, thereby creating a cycle. + */ + if (unlikely(is_file_epoll(tfile) && op == EPOLL_CTL_ADD)) { + mutex_lock(&epmutex); + did_lock_epmutex = 1; + error = -ELOOP; + if (ep_loop_check(ep, tfile) != 0) + goto error_tgt_fput; + } + + mutex_lock(&ep->mtx); /* @@ -1312,6 +1408,9 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, mutex_unlock(&ep->mtx); error_tgt_fput: + if (unlikely(did_lock_epmutex)) + mutex_unlock(&epmutex); + fput(tfile); error_fput: fput(file); @@ -1431,6 +1530,12 @@ static int __init eventpoll_init(void) EP_ITEM_COST; BUG_ON(max_user_watches < 0); + /* + * Initialize the structure used to perform epoll file descriptor + * inclusion loops checks. + */ + ep_nested_calls_init(&poll_loop_ncalls); + /* Initialize the structure used to perform safe poll wait head wake ups */ ep_nested_calls_init(&poll_safewake_ncalls); |