mirror of https://github.com/proxmox/mirror_qemu
block: make BDRV_POLL_WHILE() re-entrancy safe
Nested BDRV_POLL_WHILE() calls can occur. Currently assert(!wait_->wakeup) fails in AIO_WAIT_WHILE() when this happens. This patch converts the bool wait_->need_kick flag to an unsigned wait_->num_waiters counter. Nesting works correctly because outer AIO_WAIT_WHILE() callers evaluate the condition again after the inner caller completes (invoking the inner caller counts as aio_poll() progress). Reported-by: "fuweiwei (C)" <fuweiwei2@huawei.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Message-id: 20180307124619.6218-1-stefanha@redhat.com Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>master
parent
e4ae62b802
commit
7376eda7c2
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@ -50,8 +50,8 @@
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* }
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* }
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*/
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*/
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typedef struct {
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typedef struct {
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/* Is the main loop waiting for a kick? Accessed with atomic ops. */
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/* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */
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bool need_kick;
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unsigned num_waiters;
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} AioWait;
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} AioWait;
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/**
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/**
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@ -71,35 +71,34 @@ typedef struct {
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* wait on conditions between two IOThreads since that could lead to deadlock,
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* wait on conditions between two IOThreads since that could lead to deadlock,
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* go via the main loop instead.
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* go via the main loop instead.
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*/
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*/
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#define AIO_WAIT_WHILE(wait, ctx, cond) ({ \
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#define AIO_WAIT_WHILE(wait, ctx, cond) ({ \
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bool waited_ = false; \
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bool waited_ = false; \
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bool busy_ = true; \
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bool busy_ = true; \
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AioWait *wait_ = (wait); \
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AioWait *wait_ = (wait); \
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AioContext *ctx_ = (ctx); \
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AioContext *ctx_ = (ctx); \
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if (in_aio_context_home_thread(ctx_)) { \
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if (in_aio_context_home_thread(ctx_)) { \
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while ((cond) || busy_) { \
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while ((cond) || busy_) { \
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busy_ = aio_poll(ctx_, (cond)); \
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busy_ = aio_poll(ctx_, (cond)); \
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waited_ |= !!(cond) | busy_; \
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waited_ |= !!(cond) | busy_; \
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} \
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} \
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} else { \
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} else { \
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assert(qemu_get_current_aio_context() == \
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assert(qemu_get_current_aio_context() == \
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qemu_get_aio_context()); \
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qemu_get_aio_context()); \
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assert(!wait_->need_kick); \
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/* Increment wait_->num_waiters before evaluating cond. */ \
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/* Set wait_->need_kick before evaluating cond. */ \
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atomic_inc(&wait_->num_waiters); \
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atomic_mb_set(&wait_->need_kick, true); \
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while (busy_) { \
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while (busy_) { \
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if ((cond)) { \
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if ((cond)) { \
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waited_ = busy_ = true; \
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waited_ = busy_ = true; \
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aio_context_release(ctx_); \
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aio_context_release(ctx_); \
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aio_poll(qemu_get_aio_context(), true); \
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aio_poll(qemu_get_aio_context(), true); \
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aio_context_acquire(ctx_); \
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aio_context_acquire(ctx_); \
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} else { \
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} else { \
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busy_ = aio_poll(ctx_, false); \
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busy_ = aio_poll(ctx_, false); \
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waited_ |= busy_; \
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waited_ |= busy_; \
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} \
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} \
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} \
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} \
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atomic_dec(&wait_->num_waiters); \
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atomic_set(&wait_->need_kick, false); \
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} \
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} \
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waited_; })
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waited_; })
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/**
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/**
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@ -34,7 +34,7 @@ static void dummy_bh_cb(void *opaque)
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void aio_wait_kick(AioWait *wait)
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void aio_wait_kick(AioWait *wait)
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{
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{
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/* The barrier (or an atomic op) is in the caller. */
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/* The barrier (or an atomic op) is in the caller. */
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if (atomic_read(&wait->need_kick)) {
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if (atomic_read(&wait->num_waiters)) {
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aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
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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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}
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}
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