From patchwork Thu Jul 16 00:59:50 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kamal Mostafa X-Patchwork-Id: 496045 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id ED4B21401DA; Thu, 16 Jul 2015 11:00:35 +1000 (AEST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1ZFXXL-0002Ih-Qc; Thu, 16 Jul 2015 01:00:31 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1ZFXWj-0001sl-9R for kernel-team@lists.ubuntu.com; Thu, 16 Jul 2015 00:59:53 +0000 Received: from 1.general.kamal.us.vpn ([10.172.68.52] helo=fourier) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.76) (envelope-from ) id 1ZFXWj-0005qo-09; Thu, 16 Jul 2015 00:59:53 +0000 Received: from kamal by fourier with local (Exim 4.82) (envelope-from ) id 1ZFXWg-00085L-PI; Wed, 15 Jul 2015 17:59:50 -0700 From: Kamal Mostafa To: Brian Norris Subject: [3.19.y-ckt stable] Patch "mtd: fix: avoid race condition when accessing mtd->usecount" has been added to staging queue Date: Wed, 15 Jul 2015 17:59:50 -0700 Message-Id: <1437008390-31049-1-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 X-Extended-Stable: 3.19 Cc: Alexander Sverdlin , Giuseppe Cantavenera , Zhang Xingcai , Kamal Mostafa , kernel-team@lists.ubuntu.com X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com This is a note to let you know that I have just added a patch titled mtd: fix: avoid race condition when accessing mtd->usecount to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue This patch is scheduled to be released in version 3.19.y-ckt4. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.19.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 27cea3ce7bf803067e0685e393cb2d17e082762e Mon Sep 17 00:00:00 2001 From: Brian Norris Date: Thu, 7 May 2015 17:55:16 -0700 Subject: mtd: fix: avoid race condition when accessing mtd->usecount 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: Kamal Mostafa --- drivers/mtd/mtd_blkdevs.c | 5 +++++ 1 file changed, 5 insertions(+) -- 1.9.1 diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c index d08229e..3a69b1e 100644 --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -200,6 +200,7 @@ 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; @@ -223,6 +224,7 @@ 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; @@ -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 gendisk *disk, fmode_t mode) return; mutex_lock(&dev->lock); + mutex_lock(&mtd_table_mutex); if (--dev->open) goto unlock; @@ -259,6 +263,7 @@ static void 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); }