zram: fix umount-reset_store-mount race condition
Ganesh Mahendran was the first one who proposed to use bdev->bd_mutex to
avoid ->bd_holders race condition:
CPU0 CPU1
umount /* zram->init_done is true */
reset_store()
bdev->bd_holders == 0 mount
... zram_make_request()
zram_reset_device()
However, his solution required some considerable amount of code movement,
which we can avoid.
Apart from using bdev->bd_mutex in reset_store(), this patch also
simplifies zram_reset_device().
zram_reset_device() has a bool parameter reset_capacity which tells it
whether disk capacity and itself disk should be reset. There are two
zram_reset_device() callers:
-- zram_exit() passes reset_capacity=false
-- reset_store() passes reset_capacity=true
So we can move reset_capacity-sensitive work out of zram_reset_device()
and perform it unconditionally in reset_store(). This also lets us drop
reset_capacity parameter from zram_reset_device() and pass zram pointer
only.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit ba6b17d68c8e3aa8d55d0474299cb931965c5ea5)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3e075d6..45e2e85 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -719,7 +719,7 @@
}
}
-static void zram_reset_device(struct zram *zram, bool reset_capacity)
+static void zram_reset_device(struct zram *zram)
{
down_write(&zram->init_lock);
@@ -738,18 +738,7 @@
memset(&zram->stats, 0, sizeof(zram->stats));
zram->disksize = 0;
- if (reset_capacity)
- set_capacity(zram->disk, 0);
-
up_write(&zram->init_lock);
-
- /*
- * Revalidate disk out of the init_lock to avoid lockdep splat.
- * It's okay because disk's capacity is protected by init_lock
- * so that revalidate_disk always sees up-to-date capacity.
- */
- if (reset_capacity)
- revalidate_disk(zram->disk);
}
static ssize_t disksize_store(struct device *dev,
@@ -822,6 +811,7 @@
if (!bdev)
return -ENOMEM;
+ mutex_lock(&bdev->bd_mutex);
/* Do not reset an active device! */
if (bdev->bd_holders) {
ret = -EBUSY;
@@ -839,12 +829,17 @@
/* Make sure all pending I/O is finished */
fsync_bdev(bdev);
+ zram_reset_device(zram);
+ set_capacity(zram->disk, 0);
+
+ mutex_unlock(&bdev->bd_mutex);
+ revalidate_disk(zram->disk);
bdput(bdev);
- zram_reset_device(zram, true);
return len;
out:
+ mutex_unlock(&bdev->bd_mutex);
bdput(bdev);
return ret;
}
@@ -1147,7 +1142,7 @@
* Shouldn't access zram->disk after destroy_device
* because destroy_device already released zram->disk.
*/
- zram_reset_device(zram, false);
+ zram_reset_device(zram);
}
unregister_blkdev(zram_major, "zram");