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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: 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>
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parent
1fec117281
commit
ba6b17d68c
1 changed files with 9 additions and 14 deletions
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@ -715,7 +715,7 @@ static void zram_bio_discard(struct zram *zram, u32 index,
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}
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}
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static void zram_reset_device(struct zram *zram, bool reset_capacity)
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static void zram_reset_device(struct zram *zram)
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{
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down_write(&zram->init_lock);
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@ -734,18 +734,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
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memset(&zram->stats, 0, sizeof(zram->stats));
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zram->disksize = 0;
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if (reset_capacity)
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set_capacity(zram->disk, 0);
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up_write(&zram->init_lock);
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/*
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* Revalidate disk out of the init_lock to avoid lockdep splat.
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* It's okay because disk's capacity is protected by init_lock
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* so that revalidate_disk always sees up-to-date capacity.
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*/
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if (reset_capacity)
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revalidate_disk(zram->disk);
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}
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static ssize_t disksize_store(struct device *dev,
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@ -818,6 +807,7 @@ static ssize_t reset_store(struct device *dev,
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if (!bdev)
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return -ENOMEM;
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mutex_lock(&bdev->bd_mutex);
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/* Do not reset an active device! */
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if (bdev->bd_holders) {
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ret = -EBUSY;
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@ -835,12 +825,17 @@ static ssize_t reset_store(struct device *dev,
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/* Make sure all pending I/O is finished */
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fsync_bdev(bdev);
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zram_reset_device(zram);
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set_capacity(zram->disk, 0);
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mutex_unlock(&bdev->bd_mutex);
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revalidate_disk(zram->disk);
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bdput(bdev);
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zram_reset_device(zram, true);
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return len;
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out:
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mutex_unlock(&bdev->bd_mutex);
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bdput(bdev);
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return ret;
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}
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@ -1186,7 +1181,7 @@ static void __exit zram_exit(void)
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* Shouldn't access zram->disk after destroy_device
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* because destroy_device already released zram->disk.
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*/
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zram_reset_device(zram, false);
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zram_reset_device(zram);
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}
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unregister_blkdev(zram_major, "zram");
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