linux-kernel - Re: [PATCH] btrfs/extent_io.c: return -ENOMEM instead of BUG_ON on allocation failure in set_extent_bit if __GFP

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Date:	Thu, 05 Apr 2012 10:10:20 +0800
From:	Wang Sheng-Hui <shhuiw@...il.com>
To:	Jeff Mahoney <jeffm@...e.de>
CC:	Chris Mason <chris.mason@...cle.com>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs/extent_io.c: return -ENOMEM instead of BUG_ON on
 allocation failure in set_extent_bit if __GFP_WAIT is set in the mask

On 2012年04月04日 21:29, Jeff Mahoney wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
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> On 03/31/2012 03:25 AM, Wang Sheng-Hui wrote:
>> If __GFP_WAIT is set in the mask, set_extent_bit should return 
>> -ENOMEM to its caller to decide what to do on allocation failure, 
>> instead of BUG_ON.
>>
>> Signed-off-by: Wang Sheng-Hui <shhuiw@...il.com> --- 
>> fs/btrfs/extent_io.c |    3 ++- 1 files changed, 2 insertions(+), 1
>> deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index
>> b67814c..fd2411e 100644 --- a/fs/btrfs/extent_io.c +++
>> b/fs/btrfs/extent_io.c @@ -720,7 +720,8 @@ int
>> set_extent_bit(struct extent_io_tree *tree, u64 start, u64 end, 
>> again: if (!prealloc && (mask & __GFP_WAIT)) { prealloc =
>> alloc_extent_state(mask); -		BUG_ON(!prealloc); +		if (!prealloc) +
>> return -ENOMEM; }
>>
>> spin_lock(&tree->lock);
> 
> Hi Sheng-Hui -
> 
> Do you have a follow-on series to this? With the exception of the
> set_extent_dirty call in end_bio_extent_readpage, every set_extent_bit
> caller uses GFP_NOFS, which includes __GFP_WAIT. If we return a
> failure here, we need to catch the failure in the call sites.
> Otherwise, the failure will just be ignored and we'll end up with an
> inconsistent extent state tree.
> 
> - -Jeff
> 

Hi Jeff,

I'll review the code and provide a list of patches later.
Currently we can skip it, I think.

Thanks,
Sheng-Hui

> - -- 
> Jeff Mahoney
> SUSE Labs
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