[RFC PATCH 3/3] Restart pathwalk on rename seqcount change

[Al Viro]

On Wed, Jun 04, 2025 at 02:12:11AM +0100, Tingmao Wang wrote:
> On 6/4/25 01:55, Al Viro wrote:
> > On Wed, Jun 04, 2025 at 01:45:45AM +0100, Tingmao Wang wrote:
> >> +		rename_seqcount = read_seqbegin(&rename_lock);
> >> +		if (rename_seqcount % 2 == 1) {
> > 
> > Please, describe the condition when that can happen, preferably
> > along with a reproducer.
> 
> My understanding is that when a rename is in progress the seqcount is odd,
> is that correct?
> 
> If that's the case, then the fs_race_test in patch 2 should act as a
> reproducer, since it's constantly moving the directory.
> 
> I can add a comment to explain this, thanks for pointing out.

Please, read through the header declaring those primitives and read the
documentation it refers to - it's useful for background.

What's more, look at the area covered by rename_lock - I seriously suspect
that you are greatly overestimating it.