From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934454AbbA1EXS (ORCPT ); Tue, 27 Jan 2015 23:23:18 -0500 Received: from mail.kernel.org ([198.145.29.136]:40236 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934403AbbA1EXO (ORCPT ); Tue, 27 Jan 2015 23:23:14 -0500 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Brian Silverman , austin.linux@gmail.com, darren@dvhart.com, peterz@infradead.org, Thomas Gleixner , Zefan Li Subject: [PATCH 3.4 106/177] futex: Fix a race condition between REQUEUE_PI and task death Date: Wed, 28 Jan 2015 12:09:24 +0800 Message-Id: <1422418236-12852-197-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1422418050-12581-1-git-send-email-lizf@kernel.org> References: <1422418050-12581-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Brian Silverman 3.4.106-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 30a6b8031fe14031ab27c1fa3483cb9780e7f63c upstream. free_pi_state and exit_pi_state_list both clean up futex_pi_state's. exit_pi_state_list takes the hb lock first, and most callers of free_pi_state do too. requeue_pi doesn't, which means free_pi_state can free the pi_state out from under exit_pi_state_list. For example: task A | task B exit_pi_state_list | pi_state = | curr->pi_state_list->next | | futex_requeue(requeue_pi=1) | // pi_state is the same as | // the one in task A | free_pi_state(pi_state) | list_del_init(&pi_state->list) | kfree(pi_state) list_del_init(&pi_state->list) | Move the free_pi_state calls in requeue_pi to before it drops the hb locks which it's already holding. [ tglx: Removed a pointless free_pi_state() call and the hb->lock held debugging. The latter comes via a seperate patch ] Signed-off-by: Brian Silverman Cc: austin.linux@gmail.com Cc: darren@dvhart.com Cc: peterz@infradead.org Link: http://lkml.kernel.org/r/1414282837-23092-1-git-send-email-bsilver16384@gmail.com Signed-off-by: Thomas Gleixner [lizf: Backported to 3.4: adjust context] Signed-off-by: Zefan Li --- kernel/futex.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index fafc54f..6b320c2 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -486,8 +486,14 @@ static struct futex_pi_state * alloc_pi_state(void) return pi_state; } +/* + * Must be called with the hb lock held. + */ static void free_pi_state(struct futex_pi_state *pi_state) { + if (!pi_state) + return; + if (!atomic_dec_and_test(&pi_state->refcount)) return; @@ -1401,15 +1407,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, } retry: - if (pi_state != NULL) { - /* - * We will have to lookup the pi_state again, so free this one - * to keep the accounting correct. - */ - free_pi_state(pi_state); - pi_state = NULL; - } - ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ); if (unlikely(ret != 0)) goto out; @@ -1497,6 +1494,8 @@ retry_private: case 0: break; case -EFAULT: + free_pi_state(pi_state); + pi_state = NULL; double_unlock_hb(hb1, hb2); put_futex_key(&key2); put_futex_key(&key1); @@ -1506,6 +1505,8 @@ retry_private: goto out; case -EAGAIN: /* The owner was exiting, try again. */ + free_pi_state(pi_state); + pi_state = NULL; double_unlock_hb(hb1, hb2); put_futex_key(&key2); put_futex_key(&key1); @@ -1582,6 +1583,7 @@ retry_private: } out_unlock: + free_pi_state(pi_state); double_unlock_hb(hb1, hb2); /* @@ -1598,8 +1600,6 @@ out_put_keys: out_put_key1: put_futex_key(&key1); out: - if (pi_state != NULL) - free_pi_state(pi_state); return ret ? ret : task_count; } -- 1.9.1