Re: [PATCH V2] writeback: fix hung_task alarm when sync block

[Wanpeng Li <liwp.linux@gmail.com>]

On Wed, Jun 13, 2012 at 12:42:33PM +0800, Wanpeng Li wrote:

Hi Fengguang,

This patch need improve or ..., any comments or suggetions?

Best Regards,
Wanpeng Li

>
>From: Wanpeng Li <liwp@linux.vnet.ibm.com>
>
>"V1 -> V2"
>* remove redundant hangcheck variable
>
>I use several dd processes to write a slow SD card
>dd if=/dev/sda1 of=/dev/sdc4 bs=1M count=4000
>and several sync commands(maybe > 10),dmesg show this:
>
>[  366.888741] INFO: task sync:3518 blocked for more than 120 seconds.
>[  366.888742] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>[  366.888746] sync            D 00000201     0  3518   3462 0x00000000
>[  366.888752]  dcde5e54 00000082 00000000 00000201 00000000 c180d220 c1933d00 c1933d00
>[  366.888758]  614a7ae7 00000023 f6bc0d00 ebecb280 c180d220 f6bc0d6c f04acbfc 00000000
>[  366.888786]  f6bc0d6c dcde5e2c 00000023 f6bc0d44 00000000 00000000 ebd8b2b4 dcde5e6c
>[  366.888788] Call Trace:
>[  366.888792]  [<c107a0ee>] ? enqueue_entity+0xee/0x5a0
>[  366.888795]  [<c15abc83>] schedule+0x23/0x60
>[  366.888798]  [<c15aa5ad>] schedule_timeout+0x22d/0x2a0
>[  366.888801]  [<c1071ce2>] ? check_preempt_curr+0x72/0x90
>[  366.888804]  [<c1071d28>] ? ttwu_do_wakeup+0x28/0x130
>[  366.888807]  [<c1037f28>] ? default_spin_lock_flags+0x8/0x10
>[  366.888810]  [<c15acaad>] ? _raw_spin_lock_irqsave+0x2d/0x40
>[  366.888813]  [<c15abb17>] wait_for_common+0xa7/0x110
>[  366.888816]  [<c1074690>] ? try_to_wake_up+0x220/0x220
>[  366.888819]  [<c15abc57>] wait_for_completion+0x17/0x20
>[  366.888822]  [<c116ad80>] writeback_inodes_sb_nr+0x70/0x90
>[  366.888825]  [<c116af75>] writeback_inodes_sb+0x25/0x30
>[  366.888828]  [<c117159f>] __sync_filesystem+0x4f/0x90
>[  366.888831]  [<c11715f7>] sync_one_sb+0x17/0x20
>[  366.888834]  [<c114c430>] iterate_supers+0xc0/0xd0
>[  366.888837]  [<c11715e0>] ? __sync_filesystem+0x90/0x90
>[  366.888831]  [<c11715f7>] sync_one_sb+0x17/0x20
>[  366.888834]  [<c114c430>] iterate_supers+0xc0/0xd0
>[  366.888837]  [<c11715e0>] ? __sync_filesystem+0x90/0x90
>[  366.888840]  [<c117167b>] sys_sync+0x2b/0x60
>[  366.888842]  [<c15b385f>] sysenter_do_call+0x12/0x28
>
>Too many similar messages flood the logs. So I use a present method to
>fix this issue.
>------------------------------------------
>Author: Mark Lord <kernel@teksavvy.com>
>Date:   Fri Sep 24 09:51:13 2010 -0400
>
>    block: Prevent hang_check firing during long I/O
>------------------------------------------
>
>Signed-off-by: Wanpeng Li <liwp.linux@gmail.com>
>
>
>---
> fs/fs-writeback.c |    6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
>diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>index f2d0109..df879ee 100644
>--- a/fs/fs-writeback.c
>+++ b/fs/fs-writeback.c
>@@ -1311,7 +1311,11 @@ void writeback_inodes_sb_nr(struct super_block *sb,
> 
> 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
> 	bdi_queue_work(sb->s_bdi, &work);
>-	wait_for_completion(&done);
>+	if (sysctl_hung_task_timeout_secs)
>+		while (!wait_for_completion_timeout(&done, HZ/2))
>+			;
>+	else
>+		wait_for_completion(&done);
> }
> EXPORT_SYMBOL(writeback_inodes_sb_nr);
> 
>-- 
>1.7.9.5
>