linux-kernel - Re: [PATCH 00/29] Speculative page faults (anon vmas only)

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Date:   Sat, 1 May 2021 14:19:40 -0700
From:   Michel Lespinasse <michel@...pinasse.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Michel Lespinasse <michel@...pinasse.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux-Kernel <linux-kernel@...r.kernel.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Paul McKenney <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 00/29] Speculative page faults (anon vmas only)

Hi Ted,

On Sat, May 01, 2021 at 03:56:23PM -0400, Theodore Ts'o wrote:
> I tried running xfstests against the spf branch, and I've noticed it's
> causing regression for generic/619.  It's failing due to a umount
> failure due to a busy mount point:
> 
> QA output created by 619
> umount: /vdc: target is busy.
> 
> I haven't had a chance to investigate, but I thought I should let you know.

Thanks for the report. I think the issue is likely caused by commit
06adfeb8150d "mm: rcu safe vma->vm_file freeing", which will defer
fput on mapped files for one rcu grace period. I expect adding
synchronize_rcu to the proper place (I'm not sure exactly where though)
when unmounting file systems would be a workable fix.

Note though - at this point I am only submitting the anon part of the
patchset for inclusion. That is, the v5.12-spf-anon branch, rather
than the v5.12-spf branch which has the additional / less mature
changes for file mapped vma faults.

--
Michel "walken" Lespinasse