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

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

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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