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

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, Jun 01, 2023 at 09:45:52AM +0800, Jingbo Xu wrote:
> 
> 
> 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@linux.alibaba.com>
> >> Fixes: 9a752d18c85a ("virtiofs: add logic to free up a memory range")
> >> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > 
> > 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.

That would be great. Please test it with really small DAX window size.
Also put some pr_debug() statements to make sure you are hitting this
particular path during testing.

Thanks
Vivek