On 08/27/2010 11:28 PM, J. Bruce Fields wrote:
> From: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
> fs/fs-writeback.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> On Fri, Aug 27, 2010 at 05:06:26PM -0400, J. Bruce Fields wrote:
>> Maybe the following?
>
> I confirmed that my hang does go away after doing this.
>
> Please apply if you think this makes sense....
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 7d9d06b..81e086d 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -808,7 +808,7 @@ int bdi_writeback_thread(void *data)
> wb->last_active = jiffies;
>
> set_current_state(TASK_INTERRUPTIBLE);
> - if (!list_empty(&bdi->work_list)) {
> + if (!list_empty(&bdi->work_list) || kthread_should_stop()) {
> __set_current_state(TASK_RUNNING);
> continue;
> }
Thanks Bruce, I've applied this as well.
--
Jens Axboe
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