[PATCH][Quantal] ext4: fix crash when accessing /proc/mounts concurrently

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Wed Sep 26 13:35:18 UTC 2012

The crash was caused by a variable being erronously declared static in

In addition to /proc/mounts, the problem can also be easily replicated
by accessing /proc/fs/ext4/<partition>/options in parallel:

$ cat /proc/fs/ext4/<partition>/options > options.txt

... and then running the following command in two different terminals:

$ while diff /proc/fs/ext4/<partition>/options options.txt; do true; done

This is also the cause of the following a crash while running xfstests
#234, as reported in the following bug reports:


Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Cc: Brad Figg <brad.figg at canonical.com>
Cc: stable at vger.kernel.org
BugLink: https://bugs.launchpad.net/bugs/1053019
(cherry picked from commit 04b6f64bf52bd6d0b8dcd912e8fec8d672d44d4a,
 at git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev)
 fs/ext4/super.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index afeddd7..51d24ea 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1752,7 +1752,7 @@ static inline void ext4_show_quota_options(struct seq_file *seq,
 static const char *token2str(int token)
-	static const struct match_token *t;
+	const struct match_token *t;
 	for (t = tokens; t->token != Opt_err; t++)
 		if (t->token == token && !strchr(t->pattern, '='))

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