Re: [PATCH] btrfs: replace seed device followed by unmount causes kernel WARNING

From: Anand Jain <Anand.Jain@oracle.com>
To: linux-btrfs@vger.kernel.org
Cc: miaox@cn.fujitsu.com
Subject: Re: [PATCH] btrfs: replace seed device followed by unmount causes kernel WARNING
Date: Mon, 11 Aug 2014 17:46:26 +0800	[thread overview]
Message-ID: <53E890F2.3020004@oracle.com> (raw)
In-Reply-To: <53DA0211.4000000@oracle.com>

I have sent out the patch-set

  [PATCH 1/4] btrfs: preparatory to make btrfs_rm_dev_replace_srcdev() 
seed aware

in replacement for this patch. Kindly use/review the above patch set.

Thanks. Anand

On 31/07/2014 16:45, Anand Jain wrote:
>
>
> On 30/07/2014 15:42, Miao Xie wrote:
>> On Fri, 25 Jul 2014 20:33:34 +0800, Anand Jain wrote:
>>> After the seed device has been replaced the new target device
>>> is no more a seed device. So we need to bring that state in
>>> the fs_devices.
>>>
>>> reproducer:
>>> mount /dev/sdb /btrfs
>>> btrfs dev add /dev/sdc /btrfs
>>> btrfs rep start -B /dev/sdb /dev/sdd /btrfs
>>> umount /btrfs
>>>
>>> WARNING: CPU: 0 PID: 12661 at fs/btrfs/volumes.c:891
>>> __btrfs_close_devices+0x1b0/0x200 [btrfs]()
>>> ::
>>>
>>> __btrfs_close_devices()
>>> ::
>>>          WARN_ON(fs_devices->open_devices);
>>>          WARN_ON(fs_devices->rw_devices);
>>>
>>> per the btrfs-devlist tool (to dump fs_devices and
>>> btrfs_device from the kernel) the num_device, open_devices,
>>> rw_devices are still at 1 but the total_device is at 2,
>>> even after the seed device has been replaced in the above example.
>>>
>>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>> ---
>>>   fs/btrfs/dev-replace.c | 13 +++++++++++++
>>>   1 file changed, 13 insertions(+)
>>>
>>> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
>>> index eea26e1..a144bb1 100644
>>> --- a/fs/btrfs/dev-replace.c
>>> +++ b/fs/btrfs/dev-replace.c
>>> @@ -569,6 +569,19 @@ static int btrfs_dev_replace_finishing(struct
>>> btrfs_fs_info *fs_info,
>>>
>>>       btrfs_rm_dev_replace_blocked(fs_info);
>>>
>>> +    /*
>>> +     * if we are replacing a seed device with a writable device
>>> +     * then FS won't be a seeding FS any more.
>>> +     */
>>> +    if (src_device->fs_devices->seeding && !src_device->writeable) {
>>
>> First, why not move this code into btrfs_rm_dev_replace_srcdev()?
>>
>> Then if the first condition is true, the second
>> one(!src_device->writeable) must be true
>> because all the devices in the seed fs_device must be read-only. so
>> only the first
>> check is enough.
>>
>>> +        fs_info->fs_devices->rw_devices++;
>>
>> If src is missing dev, we would increase it twice.
>>
>>> +        fs_info->fs_devices->num_devices++;
>>> +        fs_info->fs_devices->open_devices++;
>>> +
>>> +        fs_info->fs_devices->seeding = 0;
>>> +        fs_info->fs_devices->seed = NULL;
>>
>> In fact, we may have several seed fs_devices in one fs, and the seed
>> fs_device
>> which includes src might not the first one, so assign seed to be NULL
>> would break
>> the seed fs_device list.
>
>   Yep I had question when writing this patch but later decided
>   to reset seed and seeding. if I am not wrong don't reset
>   seeding and seed will do as well.
>
> Thanks for reviewing.
> Anand
>
>> Thanks
>> Miao
>>
>>> +    }
>>> +
>>>       btrfs_rm_dev_replace_srcdev(fs_info, src_device);
>>>
>>>       btrfs_rm_dev_replace_unblocked(fs_info);
>>>
>>
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