linux-kernel - Re: [PATCH] mm/userfaultfd: Fix release hang over concurrent GUP

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Message-ID: <Z9IKhq3JDjfEEk4q@x1.local>
Date: Wed, 12 Mar 2025 18:28:22 -0400
From: Peter Xu <peterx@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Mike Rapoport <rppt@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Pavel Emelyanov <xemul@...tuozzo.com>,
	Jinjiang Tu <tujinjiang@...wei.com>,
	Dimitris Siakavaras <jimsiak@...ab.ece.ntua.gr>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] mm/userfaultfd: Fix release hang over concurrent GUP

On Wed, Mar 12, 2025 at 03:04:11PM -0700, Andrew Morton wrote:
> It would be good to have a Fixes: target but this bug seems to be so
> old that a bare cc:stable should be OK?

Yes I agree that should work for us, sorry I forgot to try attach that from
time to time..

AFAIU, such unwanted behavior (either GUP hangs, or if before commit
656710a60e36, the behavior could be a SIGBUS returned to GUP racing with
the userfaultfd_release()) should exist since the 1st day, but I didn't
verify the original commit.

Thanks,

-- 
Peter Xu