[PATCH] writeback: Fix periodic writeback after fs mount

[PATCH] writeback: Fix periodic writeback after fs mount

[Jan Kara]

Code in blkdev.c moves a device inode to default_backing_dev_info when
the last reference to the device is put and moves the device inode back
to its bdi when the first reference is acquired. This includes moving to
wb.b_dirty list if the device inode is dirty. The code however doesn't
setup timer to wake corresponding flusher thread and while wb.b_dirty
list is non-empty __mark_inode_dirty() will not set it up either. Thus
periodic writeback is effectively disabled until a sync(2) call which can
lead to unexpected data loss in case of crash or power failure.

Fix the problem by setting up a timer for periodic writeback in case we
add the first dirty inode to wb.b_dirty list in bdev_inode_switch_bdi().

Reported-by: Bert De Jonghe <Bert.DeJonghe@amplidata.com>
CC: stable@vger.kernel.org # >= 3.0
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/block_dev.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 2091db8..85f5c85 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -58,17 +58,24 @@ static void bdev_inode_switch_bdi(struct inode *inode,
 			struct backing_dev_info *dst)
 {
 	struct backing_dev_info *old = inode->i_data.backing_dev_info;
+	bool wakeup_bdi = false;
 
 	if (unlikely(dst == old))		/* deadlock avoidance */
 		return;
 	bdi_lock_two(&old->wb, &dst->wb);
 	spin_lock(&inode->i_lock);
 	inode->i_data.backing_dev_info = dst;
-	if (inode->i_state & I_DIRTY)
+	if (inode->i_state & I_DIRTY) {
+		if (bdi_cap_writeback_dirty(dst) && !wb_has_dirty_io(&dst->wb))
+			wakeup_bdi = true;
 		list_move(&inode->i_wb_list, &dst->wb.b_dirty);
+	}
 	spin_unlock(&inode->i_lock);
 	spin_unlock(&old->wb.list_lock);
 	spin_unlock(&dst->wb.list_lock);
+
+	if (wakeup_bdi)
+		bdi_wakeup_thread_delayed(dst);
 }
 
 /* Kill _all_ buffers and pagecache , dirty or not.. */
-- 
1.8.1.4

Re: [PATCH] writeback: Fix periodic writeback after fs mount

[Jan Kara]

On Thu 30-05-13 10:44:19, Jan Kara wrote:
> Code in blkdev.c moves a device inode to default_backing_dev_info when
> the last reference to the device is put and moves the device inode back
> to its bdi when the first reference is acquired. This includes moving to
> wb.b_dirty list if the device inode is dirty. The code however doesn't
> setup timer to wake corresponding flusher thread and while wb.b_dirty
> list is non-empty __mark_inode_dirty() will not set it up either. Thus
> periodic writeback is effectively disabled until a sync(2) call which can
> lead to unexpected data loss in case of crash or power failure.
> 
> Fix the problem by setting up a timer for periodic writeback in case we
> add the first dirty inode to wb.b_dirty list in bdev_inode_switch_bdi().
> 
> Reported-by: Bert De Jonghe <Bert.DeJonghe@amplidata.com>
> CC: stable@vger.kernel.org # >= 3.0
> Signed-off-by: Jan Kara <jack@suse.cz>
  Jens, I'm going over my submitted patches and I don't think you've merged
this patch. Did you?

								Honza

> ---
>  fs/block_dev.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 2091db8..85f5c85 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -58,17 +58,24 @@ static void bdev_inode_switch_bdi(struct inode *inode,
>  			struct backing_dev_info *dst)
>  {
>  	struct backing_dev_info *old = inode->i_data.backing_dev_info;
> +	bool wakeup_bdi = false;
>  
>  	if (unlikely(dst == old))		/* deadlock avoidance */
>  		return;
>  	bdi_lock_two(&old->wb, &dst->wb);
>  	spin_lock(&inode->i_lock);
>  	inode->i_data.backing_dev_info = dst;
> -	if (inode->i_state & I_DIRTY)
> +	if (inode->i_state & I_DIRTY) {
> +		if (bdi_cap_writeback_dirty(dst) && !wb_has_dirty_io(&dst->wb))
> +			wakeup_bdi = true;
>  		list_move(&inode->i_wb_list, &dst->wb.b_dirty);
> +	}
>  	spin_unlock(&inode->i_lock);
>  	spin_unlock(&old->wb.list_lock);
>  	spin_unlock(&dst->wb.list_lock);
> +
> +	if (wakeup_bdi)
> +		bdi_wakeup_thread_delayed(dst);
>  }
>  
>  /* Kill _all_ buffers and pagecache , dirty or not.. */
> -- 
> 1.8.1.4
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: [PATCH] writeback: Fix periodic writeback after fs mount

[Jens Axboe]

On Thu, Jun 27 2013, Jan Kara wrote:
> case of crash or power failure.
> > 
> > Fix the problem by setting up a timer for periodic writeback in case we
> > add the first dirty inode to wb.b_dirty list in bdev_inode_switch_bdi().
> > 
> > Reported-by: Bert De Jonghe <Bert.DeJonghe@amplidata.com>
> > CC: stable@vger.kernel.org # >= 3.0
> > Signed-off-by: Jan Kara <jack@suse.cz>
>   Jens, I'm going over my submitted patches and I don't think you've merged
> this patch. Did you?

I did not... I've added it now for 3.11, with the stable tag it should
get in the earlier ones too.

-- 
Jens Axboe