ext4: fix crash when accessing /proc/mounts concurrently

commit 50df9fd55e4271e89a7adf3b1172083dd0ca199d upstream.

The crash was caused by a variable being erronously declared static in
token2str().

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:

	https://bugs.launchpad.net/bugs/1053019
	https://bugzilla.kernel.org/show_bug.cgi?id=47731

Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c6e0cb3d1f4a9e3730aea4904037eb0e9d4dd6d8..e44b23362088d9da0ce02d95a8328420a83454ac 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1735,7 +1735,7 @@ 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, '='))