Re: [PATCH] zram: fix race between reset and mount/mkswap

Ganesh Mahendran
2015-01-31T13:29:53Z

Please ignore this.
Sorry for the noise.

2015-01-31 16:25 GMT+08:00 Ganesh Mahendran <opensource.ganesh@gmail.com>:
> Currently there is a racy between reset and mount/mkswap, so that it could
> make oops when umount a corropted filesystem.
>
> This issue can be reproduced by adding delay between bdput() and zram_reset_device
> reset_store(...) {
> bdput(bdev);
>
> msleep(2000); // test code
>
> zram_reset_device(zram, true);
> }
>
> Steps:
>
> $ echo 1 > /sys/block/zram0/reset &
> $ mount /dev/zram0 /mnt/
> $ umount /mnt
> BUG: failure at fs/buffer.c:3006/_submit_bh()!
> Kernel panic - not syncing: BUG!
> CPU: 0 PID: 726 Comm: umount Not tainted 3.19.0-rc6+ #32
> Hardware name: linux,dummy-virt (DT)
> Call trace:
> [<ffffffc00008a020>] dump_backtrace+0x0/0x124
> [<ffffffc00008a154>] show_stack+0x10/0x1c
> [<ffffffc000559514>] dump_stack+0x80/0xc4
> [<ffffffc0005587d8>] panic+0xe0/0x220
> [<ffffffc0001c7fd8>] _submit_bh+0x18c/0x1e0
> [<ffffffc0001c9c8c>] __sync_dirty_buffer+0x6c/0xfc
> [<ffffffc0001c9d28>] sync_dirty_buffer+0xc/0x18
> [<ffffffc0002205bc>] ext2_sync_super+0xa8/0xbc
> [<ffffffc000220628>] ext2_sync_fs+0x58/0x70
> [<ffffffc0001c3ab0>] sync_filesystem+0x80/0xb0
> [<ffffffc00019a294>] generic_shutdown_super+0x2c/0xd8
> [<ffffffc00019a64c>] kill_block_super+0x1c/0x70
> [<ffffffc00019a95c>] deactivate_locked_super+0x54/0x84
> [<ffffffc00019ae5c>] deactivate_super+0x8c/0x9c
> [<ffffffc0001b5fd0>] cleanup_mnt+0x38/0x84
> [<ffffffc0001b6074>] __cleanup_mnt+0xc/0x18
> [<ffffffc0000cc5bc>] task_work_run+0x94/0xec
> [<ffffffc000089d54>] do_notify_resume+0x54/0x68
> ---[ end Kernel panic - not syncing: BUG!
>
> The problem is caused by:
>
> CPU0 CPU1
> t1: bdput
> t2: mount /dev/zram0 /mnt
> t3: zram_reset_device
>
> At time 3: the mounted filesystem will be corrputed by CPU0, oops will happen
> when admin umounts /mnt or reset linux system.
>
> This patch uses bdev->bd_mutex to prevent concurrent visit of /dev/zram0.
>
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
> drivers/block/zram/zram_drv.c | 79 ++++++++++++++++++++++-------------------
> 1 file changed, 42 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index aa5a4c5..2b6b0dc 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -717,17 +717,35 @@ static void zram_bio_discard(struct zram *zram, u32 index,
> }
> }
>
> -static void zram_reset_device(struct zram *zram, bool reset_capacity)
> +static int zram_reset_device(struct zram *zram, bool reset_capacity)
> {
> - down_write(&zram->init_lock);
> + int ret;
> + struct block_device *bdev;
>
> - zram->limit_pages = 0;
> + bdev = bdget_disk(zram->disk, 0);
> + if (!bdev)
> + return -ENOMEM;
> +
> + mutex_lock(&bdev->bd_mutex);
> +
> + /* Do not reset an active device! */
> + if (bdev->bd_holders) {
> + ret = -EBUSY;
> + goto err;
> + }
> +
> + /* Make sure all pending I/O is finished */
> + fsync_bdev(bdev);
> +
> + down_write(&zram->init_lock);
>
> if (!init_done(zram)) {
> - up_write(&zram->init_lock);
> - return;
> + ret = -EIO;
> + goto err_init_done;
> }
>
> + zram->limit_pages = 0;
> +
> zcomp_destroy(zram->comp);
> zram->max_comp_streams = 1;
> zram_meta_free(zram->meta, zram->disksize);
> @@ -740,6 +758,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> set_capacity(zram->disk, 0);
>
> up_write(&zram->init_lock);
> + mutex_unlock(&bdev->bd_mutex);
> + bdput(bdev);
>
> /*
> * Revalidate disk out of the init_lock to avoid lockdep splat.
> @@ -748,6 +768,16 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
> */
> if (reset_capacity)
> revalidate_disk(zram->disk);
> +
> + return 0;
> +
> +err_init_done:
> + up_write(&zram->init_lock);
> +err:
> + mutex_unlock(&bdev->bd_mutex);
> + bdput(bdev);
> +
> + return ret;
> }
>
> static ssize_t disksize_store(struct device *dev,
> @@ -811,40 +841,19 @@ static ssize_t reset_store(struct device *dev,
> {
> int ret;
> unsigned short do_reset;
> - struct zram *zram;
> - struct block_device *bdev;
> -
> - zram = dev_to_zram(dev);
> - bdev = bdget_disk(zram->disk, 0);
> -
> - if (!bdev)
> - return -ENOMEM;
> -
> - /* Do not reset an active device! */
> - if (bdev->bd_holders) {
> - ret = -EBUSY;
> - goto out;
> - }
>
> ret = kstrtou16(buf, 10, &do_reset);
> if (ret)
> - goto out;
> + return ret;
>
> - if (!do_reset) {
> - ret = -EINVAL;
> - goto out;
> - }
> + if (!do_reset)
> + return -EINVAL;
>
> - /* Make sure all pending I/O is finished */
> - fsync_bdev(bdev);
> - bdput(bdev);
> + ret = zram_reset_device(dev_to_zram(dev), true);
> + if (ret)
> + return ret;
>
> - zram_reset_device(zram, true);
> return len;
> -
> -out:
> - bdput(bdev);
> - return ret;
> }
>
> static void __zram_make_request(struct zram *zram, struct bio *bio)
> @@ -1183,12 +1192,8 @@ static void __exit zram_exit(void)
> for (i = 0; i < num_devices; i++) {
> zram = &zram_devices[i];
>
> - destroy_device(zram);
> - /*
> - * Shouldn't access zram->disk after destroy_device
> - * because destroy_device already released zram->disk.
> - */
> zram_reset_device(zram, false);
> + destroy_device(zram);
> }
>
> unregister_blkdev(zram_major, "zram");
> --
> 1.7.9.5
>

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