linux-kernel - [37/84] ext4: don't allow ext4_free

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Message-ID: <lsq.1375276989.729223333@decadent.org.uk>
Date:	Wed, 31 Jul 2013 15:23:09 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Nagachandra P" <nagachandra@...il.com>,
	"Theodore Ts'o" <tytso@....edu>
Subject: [37/84] ext4: don't allow ext4_free_blocks() to fail due to ENOMEM

3.2.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@....edu>

commit e7676a704ee0a1ef71a6b23760b5a8f6896cb1a1 upstream.

The filesystem should not be marked inconsistent if ext4_free_blocks()
is not able to allocate memory.  Unfortunately some callers (most
notably ext4_truncate) don't have a way to reflect an error back up to
the VFS.  And even if we did, most userspace applications won't deal
with most system calls returning ENOMEM anyway.

Reported-by: Nagachandra P <nagachandra@...il.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ext4/mballoc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4696,11 +4696,16 @@ do_more:
 		 * blocks being freed are metadata. these blocks shouldn't
 		 * be used until this transaction is committed
 		 */
+	retry:
 		new_entry = kmem_cache_alloc(ext4_free_ext_cachep, GFP_NOFS);
 		if (!new_entry) {
-			ext4_mb_unload_buddy(&e4b);
-			err = -ENOMEM;
-			goto error_return;
+			/*
+			 * We use a retry loop because
+			 * ext4_free_blocks() is not allowed to fail.
+			 */
+			cond_resched();
+			congestion_wait(BLK_RW_ASYNC, HZ/50);
+			goto retry;
 		}
 		new_entry->start_cluster = bit;
 		new_entry->group  = block_group;

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