linux-kernel - Re: [PATCH 3.12 40/56] ext4: fix ext4_discard_allocated_blocks() if we can't allocate the pa struct

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Date:	Mon, 15 Sep 2014 03:46:43 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	stable@...r.kernel.org, linux-kernel@...r.kernel.org,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 3.12 40/56] ext4: fix ext4_discard_allocated_blocks() if
 we can't allocate the pa struct

On Wed, 2014-09-03 at 11:26 +0200, Jiri Slaby wrote:
> From: Theodore Ts'o <tytso@....edu>
> 
> 3.12-stable review patch.  If anyone has any objections, please let me know.
> 
> ===============
> 
> commit 86f0afd463215fc3e58020493482faa4ac3a4d69 upstream.
> 
> If there is a failure while allocating the preallocation structure, a
> number of blocks can end up getting marked in the in-memory buddy
> bitmap, and then not getting released.  This can result in the
> following corruption getting reported by the kernel:
> 
> EXT4-fs error (device sda3): ext4_mb_generate_buddy:758: group 1126,
> 12793 clusters in bitmap, 12729 in gd
> 
> In that case, we need to release the blocks using mb_free_blocks().
> 
> Tested: fs smoke test; also demonstrated that with injected errors,
> 	the file system is no longer getting corrupted
> 
> Google-Bug-Id: 16657874
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
[...]

It's a bit late now, but Ted said this introduced a regression that's
fixed by commit c99d1e6e83b0 ("ext4: fix BUG_ON in mb_free_blocks()").

(I just made the same mistake in 3.2.63.)

Ben.

-- 
Ben Hutchings
Make three consecutive correct guesses and you will be considered an expert.

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