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zram: fix umount-reset_store-mount race condition

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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>
This commit is contained in:
Sergey Senozhatsky 2015-02-12 15:00:36 -08:00 committed by Linus Torvalds
parent 1fec117281
commit ba6b17d68c
1 changed files with 9 additions and 14 deletions
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23
drivers/block/zram/zram_drv.c
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@ -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");