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7455ff1aa0
It seems that aio_wait_kick always required a memory barrier or atomic operation in the caller, but nobody actually took care of doing it. Let's put the barrier in the function instead, and pair it with another one in AIO_WAIT_WHILE. Read aio_wait_kick() comment for further explanation. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com> Message-Id: <20220524173054.12651-1-eesposit@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
87 lines
2.4 KiB
C
87 lines
2.4 KiB
C
/*
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* AioContext wait support
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*
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* Copyright (C) 2018 Red Hat, Inc.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#include "qemu/osdep.h"
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#include "qemu/main-loop.h"
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#include "block/aio-wait.h"
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AioWait global_aio_wait;
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static void dummy_bh_cb(void *opaque)
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{
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/* The point is to make AIO_WAIT_WHILE()'s aio_poll() return */
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}
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void aio_wait_kick(void)
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{
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/*
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* Paired with smp_mb in AIO_WAIT_WHILE. Here we have:
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* write(condition);
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* aio_wait_kick() {
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* smp_mb();
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* read(num_waiters);
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* }
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*
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* And in AIO_WAIT_WHILE:
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* write(num_waiters);
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* smp_mb();
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* read(condition);
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*/
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smp_mb();
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if (qatomic_read(&global_aio_wait.num_waiters)) {
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aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
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}
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}
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typedef struct {
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bool done;
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QEMUBHFunc *cb;
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void *opaque;
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} AioWaitBHData;
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/* Context: BH in IOThread */
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static void aio_wait_bh(void *opaque)
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{
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AioWaitBHData *data = opaque;
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data->cb(data->opaque);
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data->done = true;
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aio_wait_kick();
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}
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void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
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{
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AioWaitBHData data = {
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.cb = cb,
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.opaque = opaque,
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};
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assert(qemu_get_current_aio_context() == qemu_get_aio_context());
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aio_bh_schedule_oneshot(ctx, aio_wait_bh, &data);
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AIO_WAIT_WHILE(ctx, !data.done);
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}
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