Re: [PATCH] fuse: fix return value of inode_inline_reclaim_one_dmap in error path

[Jingbo Xu]

On 6/1/23 4:03 AM, Vivek Goyal wrote:
> On Mon, Apr 24, 2023 at 08:32:50PM +0800, Jingbo Xu wrote:
>> When range already got reclaimed by somebody else, return NULL so that
>> the caller could retry to allocate or reclaim another range, instead of
>> mistakenly returning the range already got reclaimed and reused by
>> others.
>>
>> Reported-by: Liu Jiang <gerry@xxxxxxxxxxxxxxxxx>
>> Fixes: 9a752d18c85a ("virtiofs: add logic to free up a memory range")
>> Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> 
> Hi Jingbo,
> 
> This patch looks correct to me.
> 
> Are you able to reproduce the problem? Or you are fixing it based on
> code inspection?

It's spotted by Liu Jiang during code review.  Not tested yet.

> 
> How are you testing this? We don't have virtiofsd DAX implementation yet
> in rust virtiofsd yet. 
> 
> I am not sure how to test this chagne now. We had out of tree patches
> in qemu and now qemu has gotten rid of C version of virtiofsd so these
> patches might not even work now.

Yeah this exception path may not be so easy to be tested as it is only
triggered in the race condition.  I have the old branch (of qemu) with
support for DAX, and maybe I could try to reproduce the exception path
by configuring limited DAX window and heavy IO workload.


-- 
Thanks,
Jingbo