Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxx>
>> Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>
>> Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
> Looks good. You can add:
> Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> 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
>>
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