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authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2015-06-25 15:00:21 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-06-25 17:00:36 -0700
commitf405c445a4866caa43101c231721123805a23bbf (patch)
treea3cf9d9ed91314ef7db9ac16a3e3d3599a1dde21 /drivers/block/zram
parent92ff15288747b80730f0132e9c98403370c27b34 (diff)
zram: close race by open overriding
[ Original patch from Minchan Kim <minchan@kernel.org> ] Commit ba6b17d68c8e ("zram: fix umount-reset_store-mount race condition") introduced bdev->bd_mutex to protect a race between mount and reset. At that time, we don't have dynamic zram-add/remove feature so it was okay. However, as we introduce dynamic device feature, bd_mutex became trouble. CPU 0 echo 1 > /sys/block/zram<id>/reset -> kernfs->s_active(A) -> zram:reset_store->bd_mutex(B) CPU 1 echo <id> > /sys/class/zram/zram-remove ->zram:zram_remove: bd_mutex(B) -> sysfs_remove_group -> kernfs->s_active(A) IOW, AB -> BA deadlock The reason we are holding bd_mutex for zram_remove is to prevent any incoming open /dev/zram[0-9]. Otherwise, we could remove zram others already have opened. But it causes above deadlock problem. To fix the problem, this patch overrides block_device.open and it returns -EBUSY if zram asserts he claims zram to reset so any incoming open will be failed so we don't need to hold bd_mutex for zram_remove ayn more. This patch is to prepare for zram-add/remove feature. [sergey.senozhatsky@gmail.com: simplify reset_store()] Signed-off-by: Minchan Kim <minchan@kernel.org> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/block/zram')
-rw-r--r--drivers/block/zram/zram_drv.c53
-rw-r--r--drivers/block/zram/zram_drv.h4
2 files changed, 38 insertions, 19 deletions
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a52a8191bb91..6a3b36d5bad6 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1070,45 +1070,60 @@ static ssize_t reset_store(struct device *dev,
struct zram *zram;
struct block_device *bdev;
+ ret = kstrtou16(buf, 10, &do_reset);
+ if (ret)
+ return ret;
+
+ if (!do_reset)
+ return -EINVAL;
+
zram = dev_to_zram(dev);
bdev = bdget_disk(zram->disk, 0);
-
if (!bdev)
return -ENOMEM;
mutex_lock(&bdev->bd_mutex);
- /* Do not reset an active device! */
- if (bdev->bd_openers) {
- ret = -EBUSY;
- goto out;
+ /* Do not reset an active device or claimed device */
+ if (bdev->bd_openers || zram->claim) {
+ mutex_unlock(&bdev->bd_mutex);
+ bdput(bdev);
+ return -EBUSY;
}
- ret = kstrtou16(buf, 10, &do_reset);
- if (ret)
- goto out;
-
- if (!do_reset) {
- ret = -EINVAL;
- goto out;
- }
+ /* From now on, anyone can't open /dev/zram[0-9] */
+ zram->claim = true;
+ mutex_unlock(&bdev->bd_mutex);
- /* Make sure all pending I/O is finished */
+ /* Make sure all the pending I/O are finished */
fsync_bdev(bdev);
zram_reset_device(zram);
-
- mutex_unlock(&bdev->bd_mutex);
revalidate_disk(zram->disk);
bdput(bdev);
+ mutex_lock(&bdev->bd_mutex);
+ zram->claim = false;
+ mutex_unlock(&bdev->bd_mutex);
+
return len;
+}
+
+static int zram_open(struct block_device *bdev, fmode_t mode)
+{
+ int ret = 0;
+ struct zram *zram;
+
+ WARN_ON(!mutex_is_locked(&bdev->bd_mutex));
+
+ zram = bdev->bd_disk->private_data;
+ /* zram was claimed to reset so open request fails */
+ if (zram->claim)
+ ret = -EBUSY;
-out:
- mutex_unlock(&bdev->bd_mutex);
- bdput(bdev);
return ret;
}
static const struct block_device_operations zram_devops = {
+ .open = zram_open,
.swap_slot_free_notify = zram_slot_free_notify,
.rw_page = zram_rw_page,
.owner = THIS_MODULE
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 042994e807cf..6dbe2df506bf 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -115,5 +115,9 @@ struct zram {
*/
u64 disksize; /* bytes */
char compressor[10];
+ /*
+ * zram is claimed so open request will be failed
+ */
+ bool claim; /* Protected by bdev->bd_mutex */
};
#endif