From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.136]:54049 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752126AbbJTAsi (ORCPT ); Mon, 19 Oct 2015 20:48:38 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Brian Norris , Zefan Li Subject: [PATCH 3.4 02/65] mtd: fix: avoid race condition when accessing mtd->usecount Date: Tue, 20 Oct 2015 08:47:12 +0800 Message-Id: <1445302095-4695-2-git-send-email-lizf@kernel.org> In-Reply-To: <1445302030-4607-1-git-send-email-lizf@kernel.org> References: <1445302030-4607-1-git-send-email-lizf@kernel.org> Sender: stable-owner@vger.kernel.org List-ID: From: Brian Norris 3.4.110-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 073db4a51ee43ccb827f54a4261c0583b028d5ab upstream. On A MIPS 32-cores machine a BUG_ON was triggered because some acesses to mtd->usecount were done without taking mtd_table_mutex. kernel: Call Trace: kernel: [] __put_mtd_device+0x20/0x50 kernel: [] blktrans_release+0x8c/0xd8 kernel: [] __blkdev_put+0x1a8/0x200 kernel: [] blkdev_close+0x1c/0x30 kernel: [] __fput+0xac/0x250 kernel: [] task_work_run+0xd8/0x120 kernel: [] work_notifysig+0x10/0x18 kernel: kernel: Code: 2442ffff ac8202d8 000217fe <00020336> dc820128 10400003 00000000 0040f809 00000000 kernel: ---[ end trace 080fbb4579b47a73 ]--- Fixed by taking the mutex in blktrans_open and blktrans_release. Note that this locking is already suggested in include/linux/mtd/blktrans.h: struct mtd_blktrans_ops { ... /* Called with mtd_table_mutex held; no race with add/remove */ int (*open)(struct mtd_blktrans_dev *dev); void (*release)(struct mtd_blktrans_dev *dev); ... }; But we weren't following it. Originally reported by (and patched by) Zhang and Giuseppe, independently. Improved and rewritten. Reported-by: Zhang Xingcai Reported-by: Giuseppe Cantavenera Tested-by: Giuseppe Cantavenera Acked-by: Alexander Sverdlin Signed-off-by: Brian Norris Signed-off-by: Zefan Li --- drivers/mtd/mtd_blkdevs.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c index f1f0671..1917f7d 100644 --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -214,6 +214,7 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode) return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/ mutex_lock(&dev->lock); + mutex_lock(&mtd_table_mutex); if (dev->open) goto unlock; @@ -237,6 +238,7 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode) unlock: dev->open++; + mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); blktrans_dev_put(dev); return ret; @@ -247,6 +249,7 @@ error_release: error_put: module_put(dev->tr->owner); kref_put(&dev->ref, blktrans_dev_release); + mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); blktrans_dev_put(dev); return ret; @@ -261,6 +264,7 @@ static int blktrans_release(struct gendisk *disk, fmode_t mode) return ret; mutex_lock(&dev->lock); + mutex_lock(&mtd_table_mutex); if (--dev->open) goto unlock; @@ -273,6 +277,7 @@ static int blktrans_release(struct gendisk *disk, fmode_t mode) __put_mtd_device(dev->mtd); } unlock: + mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); blktrans_dev_put(dev); return ret; -- 1.9.1