linux-kernel - [PATCH] remove BUG() in possible but rare condition

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Message-Id: <1334167824-19142-1-git-send-email-glommer@parallels.com>
Date:	Wed, 11 Apr 2012 15:10:24 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	<linux-kernel@...r.kernel.org>
Cc:	glommer@...allels.com, <devel@...nvz.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] remove BUG() in possible but rare condition

While stressing the kernel with with failing allocations today,
I hit the following chain of events:

alloc_page_buffers():

	bh = alloc_buffer_head(GFP_NOFS);
	if (!bh)
		goto no_grow; <= path taken

grow_dev_page():
        bh = alloc_page_buffers(page, size, 0);
        if (!bh)
                goto failed;  <= taken, consequence of the above

and then the failed path BUG()s the kernel.

The failure is inserted a litte bit artificially, but even then,
I see no reason why it should be deemed impossible in a real box.

Even though this is not a condition that we expect to see
around every time, failed allocations are expected to be handled,
and BUG() sounds just too much. As a matter of fact, grow_dev_page()
can return NULL just fine in other circumstances, so I propose we just
remove it, then.

Signed-off-by: Glauber Costa <glommer@...allels.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
---
 fs/buffer.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 36d6665..351e18e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -985,7 +985,6 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 	return page;
 
 failed:
-	BUG();
 	unlock_page(page);
 	page_cache_release(page);
 	return NULL;
-- 
1.7.7.6

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