There is no reason to use static there, and it will cause issues when
reading /proc/fs/ext4/<partition>/options concurrently.
Signed-off-by: Herton Ronaldo Krzesinski <[email protected]>
Cc: [email protected] # 3.4+
---
fs/ext4/super.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
The problem is easy to reproduce, for example running:
$ cat /proc/fs/ext4/<partition>/options > options.txt
$ while diff /proc/fs/ext4/<partition>/options options.txt; do true; done
- And concurrently on another terminal:
$ while diff /proc/fs/ext4/<partition>/options options.txt; do true; done
One of the diff loops will get incomplete options contents because of
the issue, and exit.
I also believe the same problem is the cause of the following bug:
https://bugs.launchpad.net/bugs/1053019, that happened while running
test 234 from xfstests.
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 41598ee..975405c 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1748,7 +1748,7 @@ 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, '='))
--
1.7.9.5
On Fri, Sep 21, 2012 at 10:21:00PM -0300, Herton Ronaldo Krzesinski wrote:
> There is no reason to use static there, and it will cause issues when
> reading /proc/fs/ext4/<partition>/options concurrently.
>
> Signed-off-by: Herton Ronaldo Krzesinski <[email protected]>
> Cc: [email protected] # 3.4+
Herton,
Thanks for finding the bug fix! I changed the commit descipription
slightly and have applied your patch to the ext4 tree.
- Ted
ext4: fix crash when accessing /proc/mounts concurrently
From: Herton Ronaldo Krzesinski <[email protected]>
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 <[email protected]>
Signed-off-by: "Theodore Ts'o" <[email protected]>
Cc: Brad Figg <[email protected]>
Cc: [email protected]