Re: [PATCH] Fix balance Oops

[Yan Zheng <zheng.yan@oracle.com>]

On 08/07/2009 03:19 PM, Jens Axboe wrote:
> 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.
> 

EBUSY is from the EXTENT_LOCK test in try_release_extent_state. The test
can be true is because some codes call lock_extent while corresponding
pages are not all locked. (one example is btrfs_finish_ordered_io)

Yan, Zheng