First batch of misc patches for QEMU 8.1

[PULL 19/25] qemu-coroutine: remove qatomic_mb_read()

Paolo Bonzini posted 25 patches 2 years, 9 months ago

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Maintainers: Kevin Wolf <kwolf@redhat.com>, Hanna Reitz <hreitz@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, "Alex Bennée" <alex.bennee@linaro.org>, Thomas Huth <thuth@redhat.com>, Richard Henderson <richard.henderson@linaro.org>, Helge Deller <deller@gmx.de>, Keith Busch <kbusch@kernel.org>, Klaus Jensen <its@irrelevant.dk>, "Daniel P. Berrangé" <berrange@redhat.com>, Juan Quintela <quintela@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Eric Blake <eblake@redhat.com>, Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>, Markus Armbruster <armbru@redhat.com>, Michael Roth <michael.roth@amd.com>, Peter Maydell <peter.maydell@linaro.org>, John Snow <jsnow@redhat.com>, Cleber Rosa <crosa@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Aurelien Jarno <aurelien@aurel32.net>, Jiaxun Yang <jiaxun.yang@flygoat.com>, Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>, Wainer dos Santos Moschetta <wainersm@redhat.com>, Beraldo Leal <bleal@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Ani Sinha <ani@anisinha.ca>, Gerd Hoffmann <kraxel@redhat.com>, "Marc-André Lureau" <marcandre.lureau@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

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[PULL 19/25] qemu-coroutine: remove qatomic_mb_read()

Posted by Paolo Bonzini 2 years, 9 months ago

Replace with an explicit barrier and a comment.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 util/qemu-coroutine.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c
index 849452369201..17a88f65053e 100644
--- a/util/qemu-coroutine.c
+++ b/util/qemu-coroutine.c
@@ -127,9 +127,13 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)
         Coroutine *to = QSIMPLEQ_FIRST(&pending);
         CoroutineAction ret;
 
-        /* Cannot rely on the read barrier for to in aio_co_wake(), as there are
-         * callers outside of aio_co_wake() */
-        const char *scheduled = qatomic_mb_read(&to->scheduled);
+        /*
+         * Read to before to->scheduled; pairs with qatomic_cmpxchg in
+         * qemu_co_sleep(), aio_co_schedule() etc.
+         */
+        smp_read_barrier_depends();
+
+        const char *scheduled = qatomic_read(&to->scheduled);
 
         QSIMPLEQ_REMOVE_HEAD(&pending, co_queue_next);
 
-- 
2.40.0