From: Oleg Nesterov <oleg@redhat.com>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
WangYuli <wangyuli@uniontech.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Christian Brauner <brauner@kernel.org>
Subject: Re: [RESEND PATCH] fs/pipe: Introduce a check to skip sleeping processes during pipe read/write
Date: Sun, 29 Dec 2024 14:05:43 +0100 [thread overview]
Message-ID: <20241229130543.GC27491@redhat.com> (raw)
In-Reply-To: <ee120531-5857-4bfc-908c-8a6f1f3e7385@colorfullife.com>
On 12/29, Manfred Spraul wrote:
>
> >I think that your patch (and the original patch from WangYuli) has the same
> >proble with pipe_poll()->poll_wait()->__pollwait().
>
> What is the memory barrier for pipe_poll()?
>
> There is poll_wait()->__pollwait()->add_wait_queue()->spin_unlock(). thus
> only store_release.
>
> And then READ_ONCE(), i.e. no memory barrier.
>
> Thus the CPU would be free to load pipe->head and pipe->tail before adding
> the entry to the poll table.
>
> Correct?
Yes, this was my thinking.
See also my initial reply to WangYuli
https://lore.kernel.org/all/20241226160007.GA11118@redhat.com/
Do you agree?
Oleg.
next prev parent reply other threads:[~2024-12-29 13:06 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-25 9:42 [RESEND PATCH] fs/pipe: Introduce a check to skip sleeping processes during pipe read/write WangYuli
2024-12-25 13:30 ` Andy Shevchenko
2024-12-25 13:53 ` Kent Overstreet
2024-12-25 16:04 ` Mateusz Guzik
2024-12-25 16:32 ` Kent Overstreet
2024-12-25 17:22 ` Mateusz Guzik
2024-12-25 17:41 ` Kent Overstreet
2024-12-25 15:42 ` WangYuli
2024-12-25 16:00 ` Willy Tarreau
2024-12-25 16:32 ` WangYuli
2024-12-25 16:56 ` Willy Tarreau
2024-12-26 16:00 ` Oleg Nesterov
2024-12-26 19:02 ` Linus Torvalds
2024-12-26 20:11 ` Oleg Nesterov
2024-12-26 20:29 ` Linus Torvalds
2024-12-26 20:57 ` Oleg Nesterov
2024-12-27 15:54 ` Oleg Nesterov
2024-12-27 16:43 ` Oleg Nesterov
2024-12-27 18:39 ` Manfred Spraul
2024-12-28 14:32 ` Oleg Nesterov
2024-12-28 15:22 ` Oleg Nesterov
2024-12-28 16:32 ` Oleg Nesterov
2024-12-28 18:53 ` Manfred Spraul
2024-12-29 11:54 ` Oleg Nesterov
2024-12-28 16:45 ` Manfred Spraul
2024-12-29 11:57 ` Oleg Nesterov
2024-12-29 12:41 ` Manfred Spraul
2024-12-29 13:05 ` Oleg Nesterov [this message]
2024-12-29 13:13 ` Oleg Nesterov
2024-12-29 19:54 ` Manfred Spraul
2024-12-30 15:38 ` Oleg Nesterov
2024-12-31 11:14 ` Manfred Spraul
2024-12-31 19:38 ` Linus Torvalds
2024-12-31 20:24 ` Oleg Nesterov
2024-12-31 22:31 ` Linus Torvalds
2025-01-02 13:57 ` Oleg Nesterov
2025-01-04 21:15 ` RFC: Checkpatch: Introduce list of functions that need memory barriers Manfred Spraul
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