Messages in this thread Patch in this message | | | From | lizf@kernel ... | Subject | [PATCH 3.4 02/65] mtd: fix: avoid race condition when accessing mtd->usecount | Date | Tue, 20 Oct 2015 08:47:12 +0800 |
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From: Brian Norris <computersforpeace@gmail.com>
3.4.110-rc1 review patch. If anyone has any objections, please let me know.
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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: [<ffffffff80401818>] __put_mtd_device+0x20/0x50 kernel: [<ffffffff804086f4>] blktrans_release+0x8c/0xd8 kernel: [<ffffffff802577e0>] __blkdev_put+0x1a8/0x200 kernel: [<ffffffff802579a4>] blkdev_close+0x1c/0x30 kernel: [<ffffffff8022006c>] __fput+0xac/0x250 kernel: [<ffffffff80171208>] task_work_run+0xd8/0x120 kernel: [<ffffffff8012c23c>] 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 <zhangxingcai@huawei.com> Reported-by: Giuseppe Cantavenera <giuseppe.cantavenera.ext@nokia.com> Tested-by: Giuseppe Cantavenera <giuseppe.cantavenera.ext@nokia.com> Acked-by: Alexander Sverdlin <alexander.sverdlin@nokia.com> Signed-off-by: Brian Norris <computersforpeace@gmail.com> Signed-off-by: Zefan Li <lizefan@huawei.com> --- 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
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