|From:||Greg KH <gregkh-AT-suse.de>|
|Subject:||[02/93] futex_lock_pi() key refcnt fix|
|Date:||Fri, 19 Feb 2010 08:28:55 -0800|
|Cc:||stable-review-AT-kernel.org, torvalds-AT-linux-foundation.org, akpm-AT-linux-foundation.org, alan-AT-lxorguk.ukuu.org.uk, Mikael Pettersson <mikpe-AT-it.uu.se>, Peter Zijlstra <a.p.zijlstra-AT-chello.nl>, Darren Hart <dvhltc-AT-us.ibm.com>, Thomas Gleixner <tglx-AT-linutronix.de>|
2.6.32-stable review patch. If anyone has any objections, please let us know. ------------------ From: Mikael Pettersson <firstname.lastname@example.org> 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 <email@example.com> Acked-by: Peter Zijlstra <firstname.lastname@example.org> Acked-by: Darren Hart <email@example.com> Signed-off-by: Thomas Gleixner <firstname.lastname@example.org> Signed-off-by: Greg Kroah-Hartman <email@example.com> --- kernel/futex.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1971,7 +1971,7 @@ 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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