From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:34754 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751105AbcBMXDL (ORCPT ); Sat, 13 Feb 2016 18:03:11 -0500 Subject: Patch "mtd: blkdevs: fix potential deadlock + lockdep warnings" has been added to the 4.3-stable tree To: computersforpeace@gmail.com, balbi@ti.com, gregkh@linuxfoundation.org Cc: , From: Date: Sat, 13 Feb 2016 15:03:10 -0800 Message-ID: <145540459013724@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled mtd: blkdevs: fix potential deadlock + lockdep warnings to the 4.3-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mtd-blkdevs-fix-potential-deadlock-lockdep-warnings.patch and it can be found in the queue-4.3 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From f3c63795e90f0c6238306883b6c72f14d5355721 Mon Sep 17 00:00:00 2001 From: Brian Norris Date: Mon, 26 Oct 2015 10:20:23 -0700 Subject: mtd: blkdevs: fix potential deadlock + lockdep warnings From: Brian Norris commit f3c63795e90f0c6238306883b6c72f14d5355721 upstream. Commit 073db4a51ee4 ("mtd: fix: avoid race condition when accessing mtd->usecount") fixed a race condition but due to poor ordering of the mutex acquisition, introduced a potential deadlock. The deadlock can occur, for example, when rmmod'ing the m25p80 module, which will delete one or more MTDs, along with any corresponding mtdblock devices. This could potentially race with an acquisition of the block device as follows. -> blktrans_open() -> mutex_lock(&dev->lock); -> mutex_lock(&mtd_table_mutex); -> del_mtd_device() -> mutex_lock(&mtd_table_mutex); -> blktrans_notify_remove() -> del_mtd_blktrans_dev() -> mutex_lock(&dev->lock); This is a classic (potential) ABBA deadlock, which can be fixed by making the A->B ordering consistent everywhere. There was no real purpose to the ordering in the original patch, AFAIR, so this shouldn't be a problem. This ordering was actually already present in del_mtd_blktrans_dev(), for one, where the function tried to ensure that its caller already held mtd_table_mutex before it acquired &dev->lock: if (mutex_trylock(&mtd_table_mutex)) { mutex_unlock(&mtd_table_mutex); BUG(); } So, reverse the ordering of acquisition of &dev->lock and &mtd_table_mutex so we always acquire mtd_table_mutex first. Snippets of the lockdep output follow: # modprobe -r m25p80 [ 53.419251] [ 53.420838] ====================================================== [ 53.427300] [ INFO: possible circular locking dependency detected ] [ 53.433865] 4.3.0-rc6 #96 Not tainted [ 53.437686] ------------------------------------------------------- [ 53.444220] modprobe/372 is trying to acquire lock: [ 53.449320] (&new->lock){+.+...}, at: [] del_mtd_blktrans_dev+0x80/0xdc [ 53.457271] [ 53.457271] but task is already holding lock: [ 53.463372] (mtd_table_mutex){+.+.+.}, at: [] del_mtd_device+0x18/0x100 [ 53.471321] [ 53.471321] which lock already depends on the new lock. [ 53.471321] [ 53.479856] [ 53.479856] the existing dependency chain (in reverse order) is: [ 53.487660] -> #1 (mtd_table_mutex){+.+.+.}: [ 53.492331] [] blktrans_open+0x34/0x1a4 [ 53.497879] [] __blkdev_get+0xc4/0x3b0 [ 53.503364] [] blkdev_get+0x108/0x320 [ 53.508743] [] do_dentry_open+0x218/0x314 [ 53.514496] [] path_openat+0x4c0/0xf9c [ 53.519959] [] do_filp_open+0x5c/0xc0 [ 53.525336] [] do_sys_open+0xfc/0x1cc [ 53.530716] [] ret_fast_syscall+0x0/0x1c [ 53.536375] -> #0 (&new->lock){+.+...}: [ 53.540587] [] mutex_lock_nested+0x38/0x3cc [ 53.546504] [] del_mtd_blktrans_dev+0x80/0xdc [ 53.552606] [] blktrans_notify_remove+0x7c/0x84 [ 53.558891] [] del_mtd_device+0x74/0x100 [ 53.564544] [] del_mtd_partitions+0x80/0xc8 [ 53.570451] [] mtd_device_unregister+0x24/0x48 [ 53.576637] [] spi_drv_remove+0x1c/0x34 [ 53.582207] [] __device_release_driver+0x88/0x114 [ 53.588663] [] device_release_driver+0x20/0x2c [ 53.594843] [] bus_remove_device+0xd8/0x108 [ 53.600748] [] device_del+0x10c/0x210 [ 53.606127] [] device_unregister+0xc/0x20 [ 53.611849] [] __unregister+0x10/0x20 [ 53.617211] [] device_for_each_child+0x50/0x7c [ 53.623387] [] spi_unregister_master+0x58/0x8c [ 53.629578] [] release_nodes+0x15c/0x1c8 [ 53.635223] [] __device_release_driver+0x90/0x114 [ 53.641689] [] driver_detach+0xb4/0xb8 [ 53.647147] [] bus_remove_driver+0x4c/0xa0 [ 53.652970] [] SyS_delete_module+0x11c/0x1e4 [ 53.658976] [] ret_fast_syscall+0x0/0x1c [ 53.664621] [ 53.664621] other info that might help us debug this: [ 53.664621] [ 53.672979] Possible unsafe locking scenario: [ 53.672979] [ 53.679169] CPU0 CPU1 [ 53.683900] ---- ---- [ 53.688633] lock(mtd_table_mutex); [ 53.692383] lock(&new->lock); [ 53.698306] lock(mtd_table_mutex); [ 53.704658] lock(&new->lock); [ 53.707946] [ 53.707946] *** DEADLOCK *** Fixes: 073db4a51ee4 ("mtd: fix: avoid race condition when accessing mtd->usecount") Reported-by: Felipe Balbi Tested-by: Felipe Balbi Signed-off-by: Brian Norris Signed-off-by: Greg Kroah-Hartman --- drivers/mtd/mtd_blkdevs.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -192,8 +192,8 @@ static int blktrans_open(struct block_de if (!dev) return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/ - mutex_lock(&dev->lock); mutex_lock(&mtd_table_mutex); + mutex_lock(&dev->lock); if (dev->open) goto unlock; @@ -217,8 +217,8 @@ static int blktrans_open(struct block_de unlock: dev->open++; - mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); + mutex_unlock(&mtd_table_mutex); blktrans_dev_put(dev); return ret; @@ -228,8 +228,8 @@ 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); + mutex_unlock(&mtd_table_mutex); blktrans_dev_put(dev); return ret; } @@ -241,8 +241,8 @@ static void blktrans_release(struct gend if (!dev) return; - mutex_lock(&dev->lock); mutex_lock(&mtd_table_mutex); + mutex_lock(&dev->lock); if (--dev->open) goto unlock; @@ -256,8 +256,8 @@ static void blktrans_release(struct gend __put_mtd_device(dev->mtd); } unlock: - mutex_unlock(&mtd_table_mutex); mutex_unlock(&dev->lock); + mutex_unlock(&mtd_table_mutex); blktrans_dev_put(dev); } Patches currently in stable-queue which might be from computersforpeace@gmail.com are queue-4.3/mtd-mtdpart-fix-add_mtd_partitions-error-path.patch queue-4.3/mtd-blkdevs-fix-potential-deadlock-lockdep-warnings.patch queue-4.3/mtd-nand-fix-shutdown-reboot-for-multi-chip-systems.patch queue-4.3/mtd-jz4740_nand-fix-build-on-jz4740-after-removing-gpio.h.patch