From: Richard Henderson <richard.henderson@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Cc: gshan@redhat.com, eesposit@redhat.com, david@redhat.com,
stefanha@redhat.com, cohuck@redhat.com, eauger@redhat.com
Subject: Re: [PATCH v2 8/9] async: update documentation of the memory barriers
Date: Mon, 6 Mar 2023 15:39:13 -0800 [thread overview]
Message-ID: <10e49543-b4f8-f22c-a9ab-e6340c6a0074@linaro.org> (raw)
In-Reply-To: <20230306223306.84383-9-pbonzini@redhat.com>
On 3/6/23 14:33, Paolo Bonzini wrote:
> @@ -107,11 +114,8 @@ static QEMUBH *aio_bh_dequeue(BHList *head, unsigned *flags)
> QSLIST_REMOVE_HEAD(head, next);
>
> /*
> - * The qatomic_and is paired with aio_bh_enqueue(). The implicit memory
> - * barrier ensures that the callback sees all writes done by the scheduling
> - * thread. It also ensures that the scheduling thread sees the cleared
> - * flag before bh->cb has run, and thus will call aio_notify again if
> - * necessary.
> + * Synchronizes with qatomic_fetch_or() in aio_bh_enqueue(), ensuring that
> + * the removal finishes before BH_PENDING is reset.
> */
> *flags = qatomic_fetch_and(&bh->flags,
Per this new comment, about the remove finishing first, it would seem that we need
smp_mb__before_rmw here, because QSLIST_REMOVE_HEAD is not SEQCST.
r~
next prev parent reply other threads:[~2023-03-06 23:39 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 22:32 [PATCH v2 0/9] Fix missing memory barriers on ARM Paolo Bonzini
2023-03-06 22:32 ` [PATCH v2 1/9] qatomic: add smp_mb__before/after_rmw() Paolo Bonzini
2023-03-06 22:32 ` [PATCH v2 2/9] qemu-thread-posix: cleanup, fix, document QemuEvent Paolo Bonzini
2023-03-06 22:33 ` [PATCH v2 3/9] qemu-thread-win32: " Paolo Bonzini
2023-03-06 22:33 ` [PATCH v2 4/9] edu: add smp_mb__after_rmw() Paolo Bonzini
2023-03-06 22:33 ` [PATCH v2 5/9] aio-wait: switch to smp_mb__after_rmw() Paolo Bonzini
2023-03-07 10:50 ` David Hildenbrand
2023-03-06 22:33 ` [PATCH v2 6/9] qemu-coroutine-lock: add smp_mb__after_rmw() Paolo Bonzini
2023-03-06 22:33 ` [PATCH v2 7/9] physmem: add missing memory barrier Paolo Bonzini
2023-03-06 22:33 ` [PATCH v2 8/9] async: update documentation of the memory barriers Paolo Bonzini
2023-03-06 22:48 ` Stefan Hajnoczi
2023-03-06 23:39 ` Richard Henderson [this message]
2023-03-07 10:49 ` Paolo Bonzini
2023-03-07 15:54 ` Richard Henderson
2023-03-07 17:00 ` Paolo Bonzini
2023-03-07 17:26 ` Richard Henderson
2023-03-08 10:49 ` Paolo Bonzini
2023-03-08 16:47 ` Richard Henderson
2023-03-08 18:08 ` Paolo Bonzini
2023-03-08 18:41 ` Richard Henderson
2023-03-06 22:33 ` [PATCH v2 9/9] async: clarify usage of barriers in the polling case Paolo Bonzini
2023-03-06 22:49 ` Stefan Hajnoczi
2023-03-07 10:51 ` David Hildenbrand
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