From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Nick Piggin <npiggin@gmail.com>, Peter Xu <peterx@redhat.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
John Hubbard <jhubbard@nvidia.com>, Linux-MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Michal Hocko <mhocko@suse.com>,
Kirill Shutemov <kirill@shutemov.name>,
Hugh Dickins <hughd@google.com>
Subject: Re: [RFC PATCH] mm: Fetch the dirty bit before we reset the pte
Date: Thu, 8 Oct 2020 23:02:09 +0530 [thread overview]
Message-ID: <2de084c8-9497-7877-56b3-bf1efc615e2e@linux.ibm.com> (raw)
In-Reply-To: <CAHk-=whwY0WT046fqM-zdHu9vamUjgkvmd36gCd4qSaeYy98nA@mail.gmail.com>
On 10/8/20 10:32 PM, Linus Torvalds wrote:
> On Thu, Oct 8, 2020 at 2:27 AM Aneesh Kumar K.V
> <aneesh.kumar@linux.ibm.com> wrote:
>>
>> In copy_present_page, after we mark the pte non-writable, we should
>> check for previous dirty bit updates and make sure we don't lose the dirty
>> bit on reset.
>
> No, we'll just remove that entirely.
>
> Do you have a test-case that shows a problem? I have a patch that I
> was going to delay until 5.10 because I didn't think it mattered in
> practice..
>
Unfortunately, I don't have a test case. That was observed by code
inspection while I was fixing syzkaller report.
> The second part of this patch would be to add a sequence count
> protection to fast-GUP pinning, so that GUP and fork() couldn't race,
> but I haven't written that part.
>
> Here's the first patch anyway. If you actually have a test-case where
> this matters, I guess I need to apply it now..
>
> Linus
>
-aneesh
prev parent reply other threads:[~2020-10-08 17:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-08 9:26 [RFC PATCH] mm: Fetch the dirty bit before we reset the pte Aneesh Kumar K.V
2020-10-08 17:02 ` Linus Torvalds
2020-10-08 17:06 ` Linus Torvalds
2020-10-08 17:30 ` Linus Torvalds
2020-10-08 17:32 ` Aneesh Kumar K.V [this message]
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