Re: [PATCH] Fix balance Oops

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, Aug 07 2009, Yan Zheng wrote:
> On 08/07/2009 02:50 PM, Jens Axboe wrote:
> > On Fri, Aug 07 2009, Yan Zheng wrote:
> >> invalidate_inode_pages2_range may return -EBUSY occasionally
> >> which results Oops. This patch fixes the issue by moving
> >> invalidate_inode_pages2_range into a loop and keeping calling
> >> it until the return value is not -EBUSY.
> >>
> >> Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
> >>
> >> ---
> >> diff -urp 1/fs/btrfs/relocation.c 2/fs/btrfs/relocation.c
> >> --- 1/fs/btrfs/relocation.c	2009-07-29 10:03:04.367858774 +0800
> >> +++ 2/fs/btrfs/relocation.c	2009-08-07 13:26:43.882147138 +0800
> >> @@ -2553,8 +2553,13 @@ int relocate_inode_pages(struct inode *i
> >>  	last_index = (start + len - 1) >> PAGE_CACHE_SHIFT;
> >>  
> >>  	/* make sure the dirty trick played by the caller work */
> >> -	ret = invalidate_inode_pages2_range(inode->i_mapping,
> >> -					    first_index, last_index);
> >> +	while (1) {
> >> +		ret = invalidate_inode_pages2_range(inode->i_mapping,
> >> +						    first_index, last_index);
> >> +		if (ret != -EBUSY)
> >> +			break;
> >> +		cond_resched();
> >> +	}
> > 
> > If it returns EBUSY, would it not make more sense to call
> > filemap_write_and_wait_range() instead of hammering on invalidate?
> > 
> 
> The pages to invalidate are not dirty, they are from page read-ahead.
> Actually I have no idea how invalidate_inode_pages2_range can return
> -EBUSY here. (the only user of the inode is the balancer, and it does
> not hold references to the pages)

Weird, I looked it up, and it already does a writeback wait. But I guess
that's not your issue. Patch still looks like a hack though, it would be
far better to figure out why it returns EBUSY and fix/wait appropriately
for that to pass.

-- 
Jens Axboe