Re: [PATCH v4 2/4] btrfs: cleanup btrfs_mount() using btrfs_mount_root()

[Anand Jain <anand.jain@oracle.com>]

On 01/16/2018 03:26 AM, David Sterba wrote:
> On Fri, Jan 12, 2018 at 06:14:40PM +0800, Anand Jain wrote:
>>
>> Misono,
>>
>>    This change is causing subsequent (subvol) mount to fail when device
>>    option is specified. The simplest eg for failure is ..
>>      mkfs.btrfs -qf /dev/sdc /dev/sdb
>>      mount -o device=/dev/sdb /dev/sdc /btrfs
>>      mount -o device=/dev/sdb /dev/sdc /btrfs1
>>         mount: /dev/sdc is already mounted or /btrfs1 busy
>>
>>     Looks like
>>       blkdev_get_by_path() <-- is failing.
>>       btrfs_scan_one_device()
>>       btrfs_parse_early_options()
>>       btrfs_mount()
>>
>>    Which is due to different holders (viz. btrfs_root_fs_type and
>>    btrfs_fs_type) one is used for vfs_mount and other for scan,
>>    so they form different holders and can't let EXCL open which
>>    is needed for both scan and open.
> 
> This looks close to what I see in the random test failures. I've
> reverted your patch "btrfs: optimize move uuid_mutex closer to the
> critical section" as I bisected to it. The uuid mutex around
> blkdev_get_path probably protected the concurrent mount and scan so they
> did not ask for EXCL at the same time.
> 
> Reverting (or removing the patch from the current misc-next) queue is
> simpler for me ATM as I want to get to a stable base now, we can add it
> later if we understand the issue with the mount/scan.

  Right. I don't see above test case failing on your branch [1] which
  does not have the uuid_mutex patch. Quite strange, there isn't any
  concurrency (mount and scan) in this test case.
  [1]
    git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git for-next

  Ran xfstests, got stuck at btrfs/011 failures, (and will wait for
  Liubo's v2 patch). OR is there any other test case you were referring
  to as random test failures ?

Thanks, Anand

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