Messages in this thread |  | | Subject | Re: [PATCH] locking/hung_task: Show all hung tasks before panic | From | Tetsuo Handa <> | Date | Tue, 3 Apr 2018 06:09:14 +0900 |
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Paul E. McKenney wrote: > 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> >
Thank you.
Currently sysctl_hung_task_panic case can show only the first task which was blocked for more than hung_task_timeout_secs. Suppose "there were A, B, C, D, E, F on the task_list in that order", "B was blocked for e.g. 130 seconds due to C", and "C and D were blocked for e.g. 180 seconds due to deadlock". Showing B, C, D would be more helpful than showing only B (who is just a collateral victim of a problem between C and D).
While vmcore would tell everything, it is not realistic to share vmcore of development kernels; different config / different compiler / different source / too large debuginfo / possibly confidential information etc...
Thus, I hope we can get as much information as possible via printk().
> > 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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