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:	Wed, 04 Apr 2012 09:29:44 -0400
From:	Jeff Mahoney <jeffm@...e.de>
To:	Wang Sheng-Hui <shhuiw@...il.com>
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

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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

- -- 
Jeff Mahoney
SUSE Labs
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