From: Linus Torvalds <torvalds@linux-foundation.org>
To: Eric Biggers <ebiggers@kernel.org>, Tejun Heo <tj@kernel.org>,
Zefan Li <lizefan.x@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Ingo Molnar <mingo@redhat.com>, Hillf Danton <hdanton@sina.com>,
syzbot <syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: psi_trigger_poll() is completely broken
Date: Wed, 5 Jan 2022 11:13:30 -0800 [thread overview]
Message-ID: <CAHk-=wjn5xkLWaF2_4pMVEkZrTA=LiOH=_pQK0g-_BMSE-8Jxg@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wjddvNbZBuvh9m_2VYFC1W7HvbP33mAzkPGOCHuVi5fJg@mail.gmail.com>
On Wed, Jan 5, 2022 at 11:07 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Whoever came up with that stupid "replace existing trigger with a
> write()" model should feel bad. It's garbage, and it's actively buggy
> in multiple ways.
What are the users? Can we make the rule for -EBUSY simply be that you
can _install_ a trigger, but you can't replace an existing one (except
with NULL, when you close it).
That would fix the poll() lifetime issue, and would make the
psi_trigger_replace() races fairly easy to fix - just use
if (cmpxchg(trigger_ptr, NULL, new) != NULL) {
... free 'new', return -EBUSY ..
to install the new one, instead of
rcu_assign_pointer(*trigger_ptr, new);
or something like that. No locking necessary.
But I assume people actually end up re-writing triggers, because
people are perverse and have taken advantage of this completely broken
API.
Linus
next prev parent reply other threads:[~2022-01-05 19:13 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <000000000000e8f8f505d0e479a5@google.com>
[not found] ` <20211211015620.1793-1-hdanton@sina.com>
2021-12-11 3:00 ` [syzbot] KASAN: use-after-free Read in remove_wait_queue (3) Eric Biggers
2022-01-05 15:20 ` psi_trigger_poll() is completely broken Eric Biggers
2022-01-05 18:50 ` Linus Torvalds
2022-01-05 19:07 ` Linus Torvalds
2022-01-05 19:13 ` Linus Torvalds [this message]
2022-01-06 22:05 ` Tejun Heo
2022-01-06 22:59 ` Linus Torvalds
2022-01-07 0:13 ` Eric Biggers
2022-01-07 3:02 ` Linus Torvalds
2022-01-10 13:45 ` Johannes Weiner
2022-01-10 17:25 ` Suren Baghdasaryan
2022-01-10 17:42 ` Linus Torvalds
2022-01-10 18:19 ` Suren Baghdasaryan
2022-01-11 3:02 ` Suren Baghdasaryan
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