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Subject[PATCH V2] writeback: fix hung_task alarm when sync block
Date
Hi Fengguang,

This time it works well after testing.

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


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