From 073db4a51ee43ccb827f54a4261c0583b028d5ab Mon Sep 17 00:00:00 2001 From: Brian Norris Date: Thu, 7 May 2015 17:55:16 -0700 Subject: [PATCH] mtd: fix: avoid race condition when accessing mtd->usecount 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. Cc: stable@vger.kernel.org Reported-by: Zhang Xingcai Reported-by: Giuseppe Cantavenera Tested-by: Giuseppe Cantavenera Acked-by: Alexander Sverdlin Signed-off-by: Brian Norris --- 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 2b0c52870999..df7c6c70757a 100644 --- a/drivers/mtd/mtd_blkdevs.c +++ b/drivers/mtd/mtd_blkdevs.c @@ -197,6 +197,7 @@ 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; @@ -220,6 +221,7 @@ 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; @@ -230,6 +232,7 @@ 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; @@ -243,6 +246,7 @@ 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; @@ -256,6 +260,7 @@ 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); } -- 2.20.1