Path: csiph.com!aioe.org!bofh.it!news.nic.it!robomod From: Greg Kroah-Hartman Newsgroups: linux.kernel Subject: [PATCH 4.0 52/58] mtd: fix: avoid race condition when accessing mtd->usecount Date: Sun, 19 Jul 2015 21:30:02 +0200 Message-ID: References: X-Original-To: linux-kernel@vger.kernel.org X-Mailer: git-send-email 2.4.6 User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 102 Organization: linux.* mail to news gateway X-Original-Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Zhang Xingcai , Giuseppe Cantavenera , Alexander Sverdlin , Brian Norris X-Original-Date: Sun, 19 Jul 2015 12:11:30 -0700 X-Original-Message-ID: <20150719190812.963815982@linuxfoundation.org> X-Original-References: <20150719190811.308546345@linuxfoundation.org> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: aioe.org linux.kernel:1187793 4.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Brian Norris 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: Greg Kroah-Hartman --- drivers/mtd/mtd_blkdevs.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -200,6 +200,7 @@ static int blktrans_open(struct block_de return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/ mutex_lock(&dev->lock); + mutex_lock(&mtd_table_mutex); if (dev->open) goto unlock; @@ -223,6 +224,7 @@ static int blktrans_open(struct block_de unlock: dev->open++; + mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); blktrans_dev_put(dev); return ret; @@ -233,6 +235,7 @@ 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; @@ -246,6 +249,7 @@ static void blktrans_release(struct gend return; mutex_lock(&dev->lock); + mutex_lock(&mtd_table_mutex); if (--dev->open) goto unlock; @@ -259,6 +263,7 @@ static void blktrans_release(struct gend __put_mtd_device(dev->mtd); } unlock: + mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); blktrans_dev_put(dev); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/