Re: [PATCH] btrfs: fix NPD during canceling replace when the target is missing

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

On 02/21/2018 01:04 AM, David Sterba wrote:
> On Tue, Feb 20, 2018 at 10:48:09PM +0800, Anand Jain wrote:
>> Replace target can be missing after a reboot during the replace.
>> So check if device is null.
>>
>> BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0
>> IP: btrfs_destroy_dev_replace_tgtdev+0x43/0xf0 [btrfs]
>> Call Trace:
>> btrfs_dev_replace_cancel+0x22b/0x250 [btrfs]
>> btrfs_ioctl+0x2216/0x2590 [btrfs]
>> ? do_vfs_ioctl+0x625/0x650
>> do_vfs_ioctl+0x625/0x650
>> ? security_file_ioctl+0x30/0x50
>> SyS_ioctl+0x4e/0x80
>> do_syscall_64+0x5d/0x160
>> entry_SYSCALL64_slow_path+0x25/0x25
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   fs/btrfs/dev-replace.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
>> index 87f975143c05..476981c2cf55 100644
>> --- a/fs/btrfs/dev-replace.c
>> +++ b/fs/btrfs/dev-replace.c
>> @@ -749,7 +749,8 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)
>>   		   btrfs_dev_name(src_device), src_device->devid,
>>   		   btrfs_dev_name(tgt_device));
>>   
>> -	btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);
>> +	if (tgt_device)
>> +		btrfs_destroy_dev_replace_tgtdev(fs_info, tgt_device);
> 
> I'll just discard the patch you sent a week ago that removes the 'if' in
> the first place.
> 
> https://patchwork.kernel.org/patch/10215103/

  Oops. I completely forgot about this patch! right, pls discard. If
  replace target is missing, we don't alloc a missing device as usual,
  I missed this part.

Thanks, Anand