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From: Herbert Xu <herbert@gondor.apana.org.au>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: ebiggers@kernel.org, surenb@google.com, hannes@cmpxchg.org,
	tj@kernel.org, lizefan.x@bytedance.com, mingo@redhat.com,
	peterz@infradead.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, corbet@lwn.net, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	stable@vger.kernel.org, kernel-team@android.com,
	syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com
Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
Date: Tue, 18 Jan 2022 17:58:17 +1100	[thread overview]
Message-ID: <YeZlCfZZkU5jyFS+@gondor.apana.org.au> (raw)
In-Reply-To: <CAHk-=wgwb6pJjvHYmOMT-yp5RYvw0pbv810Wcxdm5S7dWc-s0g@mail.gmail.com>

Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> Of course, in practice, for pointers, the whole "dereference off a
> pointer" on the read side *does* imply a barrier in all relevant
> situations. So yes, a smp_store_release() -> READ_ONCE() does work in
> practice, although it's technically wrong (in particular, it's wrong
> on alpha, because of the completely broken memory ordering that alpha
> has that doesn't even honor data dependencies as read-side orderings)

READ_ONCE has contained the alpha barrier since 2017:

commit 76ebbe78f7390aee075a7f3768af197ded1bdfbb
Author: Will Deacon <will@kernel.org>
Date:   Tue Oct 24 11:22:47 2017 +0100

    locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE()

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

  parent reply	other threads:[~2022-01-18  6:59 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-11  7:12 [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled Suren Baghdasaryan
2022-01-11 18:48 ` Eric Biggers
2022-01-11 19:11   ` Linus Torvalds
2022-01-11 19:26     ` Suren Baghdasaryan
2022-01-11 19:34       ` Linus Torvalds
2022-01-11 19:41     ` Eric Biggers
2022-01-11 19:45       ` Suren Baghdasaryan
2022-01-11 20:14       ` Linus Torvalds
2022-01-11 23:37         ` Suren Baghdasaryan
2022-01-12 11:06     ` Peter Zijlstra
2022-01-18  6:58     ` Herbert Xu [this message]
2022-01-12 14:37 ` Johannes Weiner

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