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authorGuenter Roeck <linux@roeck-us.net>2016-04-21 07:38:14 -0700
committerWim Van Sebroeck <wim@iguana.be>2016-05-14 16:10:33 +0200
commite1f30282a1d3d0c75d5a08e47c6ac1563065be52 (patch)
tree9017d5e8d0c076f85535af85a370363ef0e25f6c /drivers/watchdog/watchdog_dev.c
parent358d5a565fa6a5f51fcd04f8e890a0a474a814fe (diff)
downloadop-kernel-dev-e1f30282a1d3d0c75d5a08e47c6ac1563065be52.zip
op-kernel-dev-e1f30282a1d3d0c75d5a08e47c6ac1563065be52.tar.gz
watchdog: core: Fix circular locking dependency
lockdep reports the following circular locking dependency. ====================================================== INFO: possible circular locking dependency detected ] 4.6.0-rc3-00191-gfabf418 #162 Not tainted ------------------------------------------------------- systemd/1 is trying to acquire lock: ((&(&wd_data->work)->work)){+.+...}, at: [<80141650>] flush_work+0x0/0x280 but task is already holding lock: (&wd_data->lock){+.+...}, at: [<804acfa8>] watchdog_release+0x18/0x190 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&wd_data->lock){+.+...}: [<80662310>] mutex_lock_nested+0x64/0x4a8 [<804aca4c>] watchdog_ping_work+0x18/0x4c [<80143128>] process_one_work+0x1ac/0x500 [<801434b4>] worker_thread+0x38/0x554 [<80149510>] kthread+0xf4/0x108 [<80107c10>] ret_from_fork+0x14/0x24 -> #0 ((&(&wd_data->work)->work)){+.+...}: [<8017c4e8>] lock_acquire+0x70/0x90 [<8014169c>] flush_work+0x4c/0x280 [<801440f8>] __cancel_work_timer+0x9c/0x1e0 [<804acfcc>] watchdog_release+0x3c/0x190 [<8022c5e8>] __fput+0x80/0x1c8 [<80147b28>] task_work_run+0x94/0xc8 [<8010b998>] do_work_pending+0x8c/0xb4 [<80107ba8>] slow_work_pending+0xc/0x20 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&wd_data->lock); lock((&(&wd_data->work)->work)); lock(&wd_data->lock); lock((&(&wd_data->work)->work)); *** DEADLOCK *** 1 lock held by systemd/1: stack backtrace: CPU: 2 PID: 1 Comm: systemd Not tainted 4.6.0-rc3-00191-gfabf418 #162 Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) [<8010f5e4>] (unwind_backtrace) from [<8010c038>] (show_stack+0x10/0x14) [<8010c038>] (show_stack) from [<8039d7fc>] (dump_stack+0xa8/0xd4) [<8039d7fc>] (dump_stack) from [<80177ee0>] (print_circular_bug+0x214/0x334) [<80177ee0>] (print_circular_bug) from [<80179230>] (check_prevs_add+0x4dc/0x8e8) [<80179230>] (check_prevs_add) from [<8017b3d8>] (__lock_acquire+0xc6c/0x14ec) [<8017b3d8>] (__lock_acquire) from [<8017c4e8>] (lock_acquire+0x70/0x90) [<8017c4e8>] (lock_acquire) from [<8014169c>] (flush_work+0x4c/0x280) [<8014169c>] (flush_work) from [<801440f8>] (__cancel_work_timer+0x9c/0x1e0) [<801440f8>] (__cancel_work_timer) from [<804acfcc>] (watchdog_release+0x3c/0x190) [<804acfcc>] (watchdog_release) from [<8022c5e8>] (__fput+0x80/0x1c8) [<8022c5e8>] (__fput) from [<80147b28>] (task_work_run+0x94/0xc8) [<80147b28>] (task_work_run) from [<8010b998>] (do_work_pending+0x8c/0xb4) [<8010b998>] (do_work_pending) from [<80107ba8>] (slow_work_pending+0xc/0x20) Turns out the call to cancel_delayed_work_sync() in watchdog_release() is not necessary and can be dropped. If the worker is no longer necessary, the subsequent call to watchdog_update_worker() will cancel it. If it is already running, it won't do anything, since the worker function checks if it needs to ping the watchdog or not. Reported-by: Clemens Gruber <clemens.gruber@pqgruber.com> Tested-by: Clemens Gruber <clemens.gruber@pqgruber.com> Fixes: 11d7aba9ceb7 ("watchdog: imx2: Convert to use infrastructure triggered keepalives") Signed-off-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Wim Van Sebroeck <wim@iguana.be> Cc: stable <stable@vger.kernel.org>
Diffstat (limited to 'drivers/watchdog/watchdog_dev.c')
-rw-r--r--drivers/watchdog/watchdog_dev.c1
1 files changed, 0 insertions, 1 deletions
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index e2c5abb..3595cff 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -736,7 +736,6 @@ static int watchdog_release(struct inode *inode, struct file *file)
watchdog_ping(wdd);
}
- cancel_delayed_work_sync(&wd_data->work);
watchdog_update_worker(wdd);
/* make sure that /dev/watchdog can be re-opened */
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