3edf660a91
There is no need for the AioContext lock in aio_wait_bh_oneshot(). It's easy to remove the lock from existing callers and then switch from AIO_WAIT_WHILE() to AIO_WAIT_WHILE_UNLOCKED() in aio_wait_bh_oneshot(). Document that the AioContext lock should not be held across aio_wait_bh_oneshot(). Holding a lock across aio_poll() can cause deadlock so we don't want callers to do that. This is a step towards getting rid of the AioContext lock. Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Message-Id: <20230404153307.458883-1-stefanha@redhat.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com> Reviewed-by: Kevin Wolf <kwolf@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_UNLOCKED(NULL, !data.done);
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}
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