Setting the task state here may cause us to miss the wake up from
kthread_stop(), so we need to recheck kthread_should_stop() or risk
sleeping forever in the following schedule().
Symptom was an indefinite hang on an NFSv4 mount. (NFSv4 may create
multiple mounts in a temporary namespace while traversing the mount
path, and since the temporary namespace is immediately destroyed, it may
end up destroying a mount very soon after it was created, possibly
making this race more likely.)
INFO: task mount.nfs4:4314 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
mount.nfs4 D 0000000000000000 2880 4314 4313 0x00000000
ffff88001ed6da28 0000000000000046 ffff88001ed6dfd8 ffff88001ed6dfd8
ffff88001ed6c000 ffff88001ed6c000 ffff88001ed6c000 ffff88001e5003a0
ffff88001ed6dfd8 ffff88001e5003a8 ffff88001ed6c000 ffff88001ed6dfd8
Call Trace:
[<ffffffff8196090d>] schedule_timeout+0x1cd/0x2e0
[<ffffffff8106a31c>] ? mark_held_locks+0x6c/0xa0
[<ffffffff819639a0>] ? _raw_spin_unlock_irq+0x30/0x60
[<ffffffff8106a5fd>] ? trace_hardirqs_on_caller+0x14d/0x190
[<ffffffff819671fe>] ? sub_preempt_count+0xe/0xd0
[<ffffffff8195fc80>] wait_for_common+0x120/0x190
[<ffffffff81033c70>] ? default_wake_function+0x0/0x20
[<ffffffff8195fdcd>] wait_for_completion+0x1d/0x20
[<ffffffff810595fa>] kthread_stop+0x4a/0x150
[<ffffffff81061a60>] ? thaw_process+0x70/0x80
[<ffffffff810cc68a>] bdi_unregister+0x10a/0x1a0
[<ffffffff81229dc9>] nfs_put_super+0x19/0x20
[<ffffffff810ee8c4>] generic_shutdown_super+0x54/0xe0
[<ffffffff810ee9b6>] kill_anon_super+0x16/0x60
[<ffffffff8122d3b9>] nfs4_kill_super+0x39/0x90
[<ffffffff810eda45>] deactivate_locked_super+0x45/0x60
[<ffffffff810edfb9>] deactivate_super+0x49/0x70
[<ffffffff81108294>] mntput_no_expire+0x84/0xe0
[<ffffffff811084ef>] release_mounts+0x9f/0xc0
[<ffffffff81108575>] put_mnt_ns+0x65/0x80
[<ffffffff8122cc56>] nfs_follow_remote_path+0x1e6/0x420
[<ffffffff8122cfbf>] nfs4_try_mount+0x6f/0xd0
[<ffffffff8122d0c2>] nfs4_get_sb+0xa2/0x360
[<ffffffff810edcb8>] vfs_kern_mount+0x88/0x1f0
[<ffffffff810ede92>] do_kern_mount+0x52/0x130
[<ffffffff81963d9a>] ? _lock_kernel+0x6a/0x170
[<ffffffff81108e9e>] do_mount+0x26e/0x7f0
[<ffffffff81106b3a>] ? copy_mount_options+0xea/0x190
[<ffffffff811094b8>] sys_mount+0x98/0xf0
[<ffffffff810024d8>] system_call_fastpath+0x16/0x1b
1 lock held by mount.nfs4/4314:
#0: (&type->s_umount_key#24){+.+...}, at: [<ffffffff810edfb1>] deactivate_super+0x41/0x70
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Acked-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
b76b4014f9