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Commit ba6b17d6 authored by Sergey Senozhatsky's avatar Sergey Senozhatsky Committed by Linus Torvalds
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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: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: default avatarGanesh Mahendran <opensource.ganesh@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1fec1172

drivers/block/zram/zram_drv.c

+9 −14
Original line number Diff line number Diff line
@@ -715,7 +715,7 @@ static void zram_bio_discard(struct zram *zram, u32 index, 
	}

}



static void zram_reset_device(struct zram *zram, bool reset_capacity)

static void zram_reset_device(struct zram *zram)

{

	down_write(&zram->init_lock);
@@ -734,18 +734,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity) 
	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,
@@ -818,6 +807,7 @@ static ssize_t reset_store(struct device *dev, 
	if (!bdev)

		return -ENOMEM;



	mutex_lock(&bdev->bd_mutex);

	/* Do not reset an active device! */

	if (bdev->bd_holders) {

		ret = -EBUSY;
@@ -835,12 +825,17 @@ static ssize_t reset_store(struct device *dev, 


	/* 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;

}
@@ -1186,7 +1181,7 @@ static void __exit zram_exit(void) 
		 * 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");