* [PATCH V2] writeback: fix race that cause writeback hung
@ 2013-08-17 3:36 Junxiao Bi
2013-08-19 8:06 ` Jan Kara
0 siblings, 1 reply; 3+ messages in thread
From: Junxiao Bi @ 2013-08-17 3:36 UTC (permalink / raw)
To: linux-fsdevel; +Cc: jack, fengguang.wu
There is a race between mark inode dirty and writeback thread,
see the following scenario. In this case, writeback thread will
not run though there is dirty_io.
__mark_inode_dirty() bdi_writeback_workfn()
... ...
spin_lock(&inode->i_lock);
...
if (bdi_cap_writeback_dirty(bdi)) {
<<< assume wb has dirty_io, so wakeup_bdi is false.
<<< the following inode_dirty also have wakeup_bdi false.
if (!wb_has_dirty_io(&bdi->wb))
wakeup_bdi = true;
}
spin_unlock(&inode->i_lock);
<<< assume last dirty_io is removed here.
pages_written = wb_do_writeback(wb);
...
<<< work_list empty and wb has no dirty_io,
<<< delayed_work will not be queued.
if (!list_empty(&bdi->work_list) ||
(wb_has_dirty_io(wb) && dirty_writeback_interval))
queue_delayed_work(bdi_wq, &wb->dwork,
msecs_to_jiffies(dirty_writeback_interval * 10));
spin_lock(&bdi->wb.list_lock);
inode->dirtied_when = jiffies;
<<< new dirty_io is added.
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
spin_unlock(&bdi->wb.list_lock);
<<< though there is dirty_io, but wakeup_bdi is false,
<<< so writeback thread will not be waked up and
<<< the new dirty_io will not be flushed.
if (wakeup_bdi)
bdi_wakeup_thread_delayed(bdi);
Writeback will run until there is a new flush work queued.
This may cause a lot of dirty pages stay in memory for a long time.
Cc: Jan Kara <jack@suse.cz>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
---
fs/fs-writeback.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 68851ff..053ec91 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1173,6 +1173,8 @@ void __mark_inode_dirty(struct inode *inode, int flags)
bool wakeup_bdi = false;
bdi = inode_to_bdi(inode);
+ spin_unlock(&inode->i_lock);
+ spin_lock(&bdi->wb.list_lock);
if (bdi_cap_writeback_dirty(bdi)) {
WARN(!test_bit(BDI_registered, &bdi->state),
"bdi-%s not registered\n", bdi->name);
@@ -1187,8 +1189,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
wakeup_bdi = true;
}
- spin_unlock(&inode->i_lock);
- spin_lock(&bdi->wb.list_lock);
inode->dirtied_when = jiffies;
list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
spin_unlock(&bdi->wb.list_lock);
--
1.7.9.5
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH V2] writeback: fix race that cause writeback hung
2013-08-17 3:36 [PATCH V2] writeback: fix race that cause writeback hung Junxiao Bi
@ 2013-08-19 8:06 ` Jan Kara
2013-08-21 1:32 ` Junxiao Bi
0 siblings, 1 reply; 3+ messages in thread
From: Jan Kara @ 2013-08-19 8:06 UTC (permalink / raw)
To: Junxiao Bi; +Cc: linux-fsdevel, jack, fengguang.wu
On Sat 17-08-13 11:36:03, Junxiao Bi wrote:
> There is a race between mark inode dirty and writeback thread,
> see the following scenario. In this case, writeback thread will
> not run though there is dirty_io.
>
> __mark_inode_dirty() bdi_writeback_workfn()
> ... ...
> spin_lock(&inode->i_lock);
> ...
> if (bdi_cap_writeback_dirty(bdi)) {
> <<< assume wb has dirty_io, so wakeup_bdi is false.
> <<< the following inode_dirty also have wakeup_bdi false.
> if (!wb_has_dirty_io(&bdi->wb))
> wakeup_bdi = true;
> }
> spin_unlock(&inode->i_lock);
> <<< assume last dirty_io is removed here.
> pages_written = wb_do_writeback(wb);
> ...
> <<< work_list empty and wb has no dirty_io,
> <<< delayed_work will not be queued.
> if (!list_empty(&bdi->work_list) ||
> (wb_has_dirty_io(wb) && dirty_writeback_interval))
> queue_delayed_work(bdi_wq, &wb->dwork,
> msecs_to_jiffies(dirty_writeback_interval * 10));
> spin_lock(&bdi->wb.list_lock);
> inode->dirtied_when = jiffies;
> <<< new dirty_io is added.
> list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
> spin_unlock(&bdi->wb.list_lock);
>
> <<< though there is dirty_io, but wakeup_bdi is false,
> <<< so writeback thread will not be waked up and
> <<< the new dirty_io will not be flushed.
> if (wakeup_bdi)
> bdi_wakeup_thread_delayed(bdi);
>
> Writeback will run until there is a new flush work queued.
> This may cause a lot of dirty pages stay in memory for a long time.
>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Fengguang Wu <fengguang.wu@intel.com>
> Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/fs-writeback.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 68851ff..053ec91 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1173,6 +1173,8 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> bool wakeup_bdi = false;
> bdi = inode_to_bdi(inode);
>
> + spin_unlock(&inode->i_lock);
> + spin_lock(&bdi->wb.list_lock);
> if (bdi_cap_writeback_dirty(bdi)) {
> WARN(!test_bit(BDI_registered, &bdi->state),
> "bdi-%s not registered\n", bdi->name);
> @@ -1187,8 +1189,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> wakeup_bdi = true;
> }
>
> - spin_unlock(&inode->i_lock);
> - spin_lock(&bdi->wb.list_lock);
> inode->dirtied_when = jiffies;
> list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
> spin_unlock(&bdi->wb.list_lock);
> --
> 1.7.9.5
>
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH V2] writeback: fix race that cause writeback hung
2013-08-19 8:06 ` Jan Kara
@ 2013-08-21 1:32 ` Junxiao Bi
0 siblings, 0 replies; 3+ messages in thread
From: Junxiao Bi @ 2013-08-21 1:32 UTC (permalink / raw)
To: Jan Kara; +Cc: linux-fsdevel, fengguang.wu, viro
Cc: Al Viro <viro@zeniv.linux.org.uk>
On 08/19/2013 04:06 PM, Jan Kara wrote:
> On Sat 17-08-13 11:36:03, Junxiao Bi wrote:
>> There is a race between mark inode dirty and writeback thread,
>> see the following scenario. In this case, writeback thread will
>> not run though there is dirty_io.
>>
>> __mark_inode_dirty() bdi_writeback_workfn()
>> ... ...
>> spin_lock(&inode->i_lock);
>> ...
>> if (bdi_cap_writeback_dirty(bdi)) {
>> <<< assume wb has dirty_io, so wakeup_bdi is false.
>> <<< the following inode_dirty also have wakeup_bdi false.
>> if (!wb_has_dirty_io(&bdi->wb))
>> wakeup_bdi = true;
>> }
>> spin_unlock(&inode->i_lock);
>> <<< assume last dirty_io is removed here.
>> pages_written = wb_do_writeback(wb);
>> ...
>> <<< work_list empty and wb has no dirty_io,
>> <<< delayed_work will not be queued.
>> if (!list_empty(&bdi->work_list) ||
>> (wb_has_dirty_io(wb) && dirty_writeback_interval))
>> queue_delayed_work(bdi_wq, &wb->dwork,
>> msecs_to_jiffies(dirty_writeback_interval * 10));
>> spin_lock(&bdi->wb.list_lock);
>> inode->dirtied_when = jiffies;
>> <<< new dirty_io is added.
>> list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
>> spin_unlock(&bdi->wb.list_lock);
>>
>> <<< though there is dirty_io, but wakeup_bdi is false,
>> <<< so writeback thread will not be waked up and
>> <<< the new dirty_io will not be flushed.
>> if (wakeup_bdi)
>> bdi_wakeup_thread_delayed(bdi);
>>
>> Writeback will run until there is a new flush work queued.
>> This may cause a lot of dirty pages stay in memory for a long time.
>>
>> Cc: Jan Kara <jack@suse.cz>
>> Cc: Fengguang Wu <fengguang.wu@intel.com>
>> Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
> Looks good. You can add:
> Reviewed-by: Jan Kara <jack@suse.cz>
>
> Honza
>
>> ---
>> fs/fs-writeback.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>> index 68851ff..053ec91 100644
>> --- a/fs/fs-writeback.c
>> +++ b/fs/fs-writeback.c
>> @@ -1173,6 +1173,8 @@ void __mark_inode_dirty(struct inode *inode, int flags)
>> bool wakeup_bdi = false;
>> bdi = inode_to_bdi(inode);
>>
>> + spin_unlock(&inode->i_lock);
>> + spin_lock(&bdi->wb.list_lock);
>> if (bdi_cap_writeback_dirty(bdi)) {
>> WARN(!test_bit(BDI_registered, &bdi->state),
>> "bdi-%s not registered\n", bdi->name);
>> @@ -1187,8 +1189,6 @@ void __mark_inode_dirty(struct inode *inode, int flags)
>> wakeup_bdi = true;
>> }
>>
>> - spin_unlock(&inode->i_lock);
>> - spin_lock(&bdi->wb.list_lock);
>> inode->dirtied_when = jiffies;
>> list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
>> spin_unlock(&bdi->wb.list_lock);
>> --
>> 1.7.9.5
>>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-08-19 8:06 ` Jan Kara
2013-08-21 1:32 ` Junxiao Bi
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