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| author | Brian Norris <computersforpeace@gmail.com> | 2015-05-07 17:55:16 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-07-21 10:10:14 -0700 |
| commit | 4c5f659b4ce744621371ca60590a37f1781ada8e (patch) | |
| tree | fe8d4a83db1f00187465b42e3f28986bdc5160f8 | |
| parent | 5db972ac2102a2efe0525ef82fc474fe84d46c76 (diff) | |
| download | lwn-4c5f659b4ce744621371ca60590a37f1781ada8e.tar.gz lwn-4c5f659b4ce744621371ca60590a37f1781ada8e.zip | |
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: [<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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/mtd/mtd_blkdevs.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c index d08229eb44d8..3a69b1e56908 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); } |