Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled

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To: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Tue, 11 Jan 2022 11:34:53 -0800
Cc: Eric Biggers <ebiggers@xxxxxxxxxx>, Johannes Weiner <hannes@xxxxxxxxxxx>, Tejun Heo <tj@xxxxxxxxxx>, Zefan Li <lizefan.x@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Juri Lelli <juri.lelli@xxxxxxxxxx>, Vincent Guittot <vincent.guittot@xxxxxxxxxx>, Dietmar Eggemann <dietmar.eggemann@xxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Ben Segall <bsegall@xxxxxxxxxx>, Mel Gorman <mgorman@xxxxxxx>, Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, "open list:DOCUMENTATION" <linux-doc@xxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Cgroups <cgroups@xxxxxxxxxxxxxxx>, stable <stable@xxxxxxxxxxxxxxx>, Android Kernel Team <kernel-team@xxxxxxxxxxx>, syzbot <syzbot+cdb5dd11c97cc532efad@xxxxxxxxxxxxxxxxxxxxxxxxx>
In-reply-to: <CAJuCfpE3feNU=36qRUdCJsk41rxQBv1gRYy5R1dB1djMd0NLjg@mail.gmail.com>
References: <20220111071212.1210124-1-surenb@google.com> <Yd3RClhoz24rrU04@sol.localdomain> <CAHk-=wgwb6pJjvHYmOMT-yp5RYvw0pbv810Wcxdm5S7dWc-s0g@mail.gmail.com> <CAJuCfpE3feNU=36qRUdCJsk41rxQBv1gRYy5R1dB1djMd0NLjg@mail.gmail.com>

On Tue, Jan 11, 2022 at 11:27 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
>
> Thanks for the explanation!
> So, it sounds like the best (semantically correct) option I have here
> is smp_store_release() to set the pointer, and then smp_load_acquire()
> to read it. Is my understanding correct?

Yeah, that's the clearest one from a memory ordering standpoint, and
is generally also cheap.

                Linus

References:
- [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
  - From: Suren Baghdasaryan
- Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
  - From: Eric Biggers
- Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
  - From: Linus Torvalds
- Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
  - From: Suren Baghdasaryan

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