Messages in this thread Patch in this message | | | Date | Tue, 30 Mar 2010 15:57:06 -0700 | From | Greg KH <> | Subject | [04/89] futex_lock_pi() key refcnt fix |
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2.6.31-stable review patch. If anyone has any objections, please let us know.
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From: Mikael Pettersson <mikpe@it.uu.se>
commit 5ecb01cfdf96c5f465192bdb2a4fd4a61a24c6cc upstream.
This fixes a futex key reference count bug in futex_lock_pi(), where a key's reference count is incremented twice but decremented only once, causing the backing object to not be released.
If the futex is created in a temporary file in an ext3 file system, this bug causes the file's inode to become an "undead" orphan, which causes an oops from a BUG_ON() in ext3_put_super() when the file system is unmounted. glibc's test suite is known to trigger this, see <http://bugzilla.kernel.org/show_bug.cgi?id=14256>.
The bug is a regression from 2.6.28-git3, namely Peter Zijlstra's 38d47c1b7075bd7ec3881141bb3629da58f88dab "[PATCH] futex: rely on get_user_pages() for shared futexes". That commit made get_futex_key() also increment the reference count of the futex key, and updated its callers to decrement the key's reference count before returning. Unfortunately the normal exit path in futex_lock_pi() wasn't corrected: the reference count is incremented by get_futex_key() and queue_lock(), but the normal exit path only decrements once, via unqueue_me_pi(). The fix is to put_futex_key() after unqueue_me_pi(), since 2.6.31 this is easily done by 'goto out_put_key' rather than 'goto out'.
Signed-off-by: Mikael Pettersson <mikpe@it.uu.se> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Darren Hart <dvhltc@us.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/futex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/futex.c +++ b/kernel/futex.c @@ -1974,7 +1974,7 @@ retry_private: /* Unqueue and drop the lock */ unqueue_me_pi(&q); - goto out; + goto out_put_key; out_unlock_put_key: queue_unlock(&q, hb);
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