Messages in this thread |  | | Date | Mon, 2 Apr 2018 08:35:30 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] locking/hung_task: Show all hung tasks before panic |
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On Mon, Apr 02, 2018 at 11:12:04PM +0900, Tetsuo Handa wrote: > When we get a hung task it can often be valuable to see _all_ the hung > tasks on the system before calling panic(). > > Quoting from https://syzkaller.appspot.com/text?tag=CrashReport&id=5412451675799552 > ---------------------------------------- > INFO: task syz-executor3:13421 blocked for more than 120 seconds. > Not tainted 4.16.0-rc7+ #9 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > syz-executor3 D24672 13421 4481 0x00000004 > Call Trace: > context_switch kernel/sched/core.c:2862 [inline] > __schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440 > schedule+0xf5/0x430 kernel/sched/core.c:3499 > __rwsem_down_read_failed_common kernel/locking/rwsem-xadd.c:269 [inline] > rwsem_down_read_failed+0x401/0x6e0 kernel/locking/rwsem-xadd.c:286 > call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94 > __down_read arch/x86/include/asm/rwsem.h:83 [inline] > down_read+0xa4/0x150 kernel/locking/rwsem.c:26 > __get_super.part.9+0x1d3/0x280 fs/super.c:663 > __get_super include/linux/spinlock.h:310 [inline] > get_super+0x2d/0x40 fs/super.c:692 > fsync_bdev+0x19/0x80 fs/block_dev.c:468 > invalidate_partition+0x35/0x60 block/genhd.c:1566 > drop_partitions.isra.12+0xcd/0x1d0 block/partition-generic.c:440 > rescan_partitions+0x72/0x900 block/partition-generic.c:513 > __blkdev_reread_part+0x15f/0x1e0 block/ioctl.c:173 > blkdev_reread_part+0x26/0x40 block/ioctl.c:193 > loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:619 > loop_set_status+0x9bb/0xf60 drivers/block/loop.c:1161 > loop_set_status64+0x9d/0x110 drivers/block/loop.c:1271 > lo_ioctl+0xd86/0x1b70 drivers/block/loop.c:1381 > (...snipped...) > Showing all locks held in the system: > (...snipped...) > 3 locks held by syz-executor3/13421: > #0: (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000834f78af>] lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355 /* mutex_lock_nested(&lo->lo_ctl_mutex, 1); */ > #1: (&bdev->bd_mutex){+.+.}, at: [<0000000003605603>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:192 > #2: (&type->s_umount_key#77){.+.+}, at: [<0000000077701649>] __get_super.part.9+0x1d3/0x280 fs/super.c:663 /* down_read(&sb->s_umount); */ > (...snipped...) > 2 locks held by syz-executor0/13428: > #0: (&type->s_umount_key#76/1){+.+.}, at: [<00000000d25ba33a>] alloc_super fs/super.c:211 [inline] > #0: (&type->s_umount_key#76/1){+.+.}, at: [<00000000d25ba33a>] sget_userns+0x3a1/0xe40 fs/super.c:502 /* down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING); */ > #1: (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000834f78af>] lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355 /* mutex_lock_nested(&lo->lo_ctl_mutex, 1); */ > ---------------------------------------- > > In addition to showing hashed address of lock instances, it would be > nice if trace of 13428 is printed as well as 13421. > > Showing hung tasks up to /proc/sys/kernel/hung_task_warnings could delay > calling panic() but normally there should not be so many hung tasks. > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Cc: Vegard Nossum <vegard.nossum@oracle.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Mandeep Singh Baines <msb@chromium.org> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
I just know that I am going to regret this the first time this happens on a low-speed console port, but...
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@kernel.org> > --- > kernel/hung_task.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/kernel/hung_task.c b/kernel/hung_task.c > index 751593e..32b4794 100644 > --- a/kernel/hung_task.c > +++ b/kernel/hung_task.c > @@ -44,6 +44,7 @@ > > static int __read_mostly did_panic; > static bool hung_task_show_lock; > +static bool hung_task_call_panic; > > static struct task_struct *watchdog_task; > > @@ -127,10 +128,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) > touch_nmi_watchdog(); > > if (sysctl_hung_task_panic) { > - if (hung_task_show_lock) > - debug_show_all_locks(); > - trigger_all_cpu_backtrace(); > - panic("hung_task: blocked tasks"); > + hung_task_show_lock = true; > + hung_task_call_panic = true; > } > } > > @@ -193,6 +192,10 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) > rcu_read_unlock(); > if (hung_task_show_lock) > debug_show_all_locks(); > + if (hung_task_call_panic) { > + trigger_all_cpu_backtrace(); > + panic("hung_task: blocked tasks"); > + } > } > > static long hung_timeout_jiffies(unsigned long last_checked, > -- > 1.8.3.1 >
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