| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.6 078/100] watchdog: core: Fix circular locking dependency | Date | Mon, 30 May 2016 13:50:13 -0700 |
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4.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Guenter Roeck <linux@roeck-us.net>
commit e1f30282a1d3d0c75d5a08e47c6ac1563065be52 upstream.
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));
--- drivers/watchdog/watchdog_dev.c | 1 - 1 file changed, 1 deletion(-)
--- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -736,7 +736,6 @@ static int watchdog_release(struct inode 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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