Re: [PATCH] btrfs: remove spurious WARN_ON(ref->count) in find_parent_nodes

[Lu Fengqi <lufq.fnst@cn.fujitsu.com>]

On Mon, Jan 22, 2018 at 02:38:42PM +0200, Nikolay Borisov wrote:
>
>
>On 22.01.2018 14:19, Lu Fengqi wrote:
>> On 01/22/2018 04:46 PM, Nikolay Borisov wrote:
>>>
>>>
>>> On 22.01.2018 05:34, Lu Fengqi wrote:
>>>> According to my bisect result, The frequency of the warning occurrence
>>>> increased to the detectable degree after this patch
>>>
>>> That sentence implies that even before Ed's patch it was possible to
>>> trigger those warnings, is that true? Personally I've never seen such
>>> warnings while executing btrfs/004. How do you configure the filesystem
>>> for the test runs?
>>>
>> 
>> Just only default mount option.
>> 
>> ➜  xfstests-dev git:(master) for i in $(seq 1 100); do echo $i; if !
>> sudo ./check btrfs/004; then break; fi; done
>> 1
>> 
>> FSTYP         -- btrfs
>> 
>> PLATFORM      -- Linux/x86_64 sarch 4.15.0-rc9
>> 
>> MKFS_OPTIONS  -- /dev/vdd1
>> 
>> MOUNT_OPTIONS -- /dev/vdd1 /mnt/scratch
>> 
>> 
>> 
>> 
>> btrfs/004 47s ... 49s
>> 
>> Ran: btrfs/004
>> 
>> Passed all 1 tests
>> 
>> 
>> 
>> 
>> 2
>> 
>> FSTYP         -- btrfs
>> 
>> PLATFORM      -- Linux/x86_64 sarch 4.15.0-rc9
>> 
>> MKFS_OPTIONS  -- /dev/vdd1
>> 
>> MOUNT_OPTIONS -- /dev/vdd1 /mnt/scratch
>> 
>> 
>> 
>> 
>> btrfs/004 49s ... 52s
>> 
>> _check_dmesg: something found in dmesg (see
>> /home/luke/workspace/xfstests-dev/results//btrfs/004.dmesg)
>> 
>> Ran: btrfs/004
>> 
>> Failures: btrfs/004
>> 
>> Failed 1 of 1 tests
>> 
>> The probability of this warning appearing is rather low, and I only
>> encountered 52 warnings when I looped 1008 times btrfs/004 for 20 hours
>> in 4.15-rc6 (IOW, the probability is nearly 5%). So you want to trigger
>> warning also need more luck or patience.
>
>Thanks but is this before or after the mentioned commit below?
>

After this commit. The bisect condition I use to locate this commit is
to repeat btrfs/004 20 times without warning (This may not be accurate enough,
can only be used as a reference). Maybe Zygo has found a finer way to reproduce
it, so he reproduce this warning more frequently than me.

>
>> 
>>>> 86d5f9944252 ("btrfs: convert prelimary reference tracking to use
>>>> rbtrees")
>>>> is committed. I understand that this does not mean that this patch
>>>> caused
>>>> the problem, but maybe Edmund can give us some help, so I added him
>>>> to the
>>>> recipient.
>>>
>>>
>> 
>> 
>
>

-- 
Thanks,
Lu