4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> [ Upstream commit 401c636a0eeb0d51862fce222da1bf08e3a0ffd0 ] 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=5316056503549952 ---------------------------------------- INFO: task syz-executor0:6540 blocked for more than 120 seconds. Not tainted 4.16.0+ #13 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor0 D23560 6540 4521 0x80000004 Call Trace: context_switch kernel/sched/core.c:2848 [inline] __schedule+0x8fb/0x1ef0 kernel/sched/core.c:3490 schedule+0xf5/0x430 kernel/sched/core.c:3549 schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3607 __mutex_lock_common kernel/locking/mutex.c:833 [inline] __mutex_lock+0xb7f/0x1810 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355 __blkdev_driver_ioctl block/ioctl.c:303 [inline] blkdev_ioctl+0x1759/0x1e00 block/ioctl.c:601 ioctl_by_bdev+0xa5/0x110 fs/block_dev.c:2060 isofs_get_last_session fs/isofs/inode.c:567 [inline] isofs_fill_super+0x2ba9/0x3bc0 fs/isofs/inode.c:660 mount_bdev+0x2b7/0x370 fs/super.c:1119 isofs_mount+0x34/0x40 fs/isofs/inode.c:1560 mount_fs+0x66/0x2d0 fs/super.c:1222 vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037 vfs_kern_mount fs/namespace.c:2514 [inline] do_new_mount fs/namespace.c:2517 [inline] do_mount+0xea4/0x2b90 fs/namespace.c:2847 ksys_mount+0xab/0x120 fs/namespace.c:3063 SYSC_mount fs/namespace.c:3077 [inline] SyS_mount+0x39/0x50 fs/namespace.c:3074 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 (...snipped...) Showing all locks held in the system: (...snipped...) 2 locks held by syz-executor0/6540: #0: 00000000566d4c39 (&type->s_umount_key#49/1){+.+.}, at: alloc_super fs/super.c:211 [inline] #0: 00000000566d4c39 (&type->s_umount_key#49/1){+.+.}, at: sget_userns+0x3b2/0xe60 fs/super.c:502 /* down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING); */ #1: 0000000043ca8836 (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355 /* mutex_lock_nested(&lo->lo_ctl_mutex, 1); */ (...snipped...) 3 locks held by syz-executor7/6541: #0: 0000000043ca8836 (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355 /* mutex_lock_nested(&lo->lo_ctl_mutex, 1); */ #1: 000000007bf3d3f9 (&bdev->bd_mutex){+.+.}, at: blkdev_reread_part+0x1e/0x40 block/ioctl.c:192 #2: 00000000566d4c39 (&type->s_umount_key#50){.+.+}, at: __get_super.part.10+0x1d3/0x280 fs/super.c:663 /* down_read(&sb->s_umount); */ ---------------------------------------- When reporting an AB-BA deadlock like shown above, it would be nice if trace of PID=6541 is printed as well as trace of PID=6540 before calling panic(). 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. Link: http://lkml.kernel.org/r/201804050705.BHE57833.HVFOFtSOMQJFOL@xxxxxxxxxxxxxxxxxxx Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx> Cc: Mandeep Singh Baines <msb@xxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/hung_task.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -44,6 +44,7 @@ int __read_mostly sysctl_hung_task_warni 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_ 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_t 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,
