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authorPaolo Bonzini <pbonzini@redhat.com>2017-01-12 19:07:53 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2017-01-16 13:25:17 +0000
commitd7c99a1282ca2de1c344b8aa91be5364e9c6aa8f (patch)
treee7ea12e8f68e634eb89b7a4f98c739442f6745b6 /async.c
parent51dee5e465e1b3454a886792ca3e14b851e8e67d (diff)
downloadqemu-arm-d7c99a1282ca2de1c344b8aa91be5364e9c6aa8f.tar.gz
aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh
This will make it possible to walk the list of bottom halves without holding the AioContext lock---and in turn to call bottom half handlers without holding the lock. Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Message-id: 20170112180800.21085-4-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'async.c')
-rw-r--r--async.c35
1 files changed, 16 insertions, 19 deletions
diff --git a/async.c b/async.c
index 69292faf13..2305e11f26 100644
--- a/async.c
+++ b/async.c
@@ -53,14 +53,14 @@ void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
.cb = cb,
.opaque = opaque,
};
- qemu_mutex_lock(&ctx->list_lock);
+ qemu_lockcnt_lock(&ctx->list_lock);
bh->next = ctx->first_bh;
bh->scheduled = 1;
bh->deleted = 1;
/* Make sure that the members are ready before putting bh into list */
smp_wmb();
ctx->first_bh = bh;
- qemu_mutex_unlock(&ctx->list_lock);
+ qemu_lockcnt_unlock(&ctx->list_lock);
aio_notify(ctx);
}
@@ -73,12 +73,12 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
.cb = cb,
.opaque = opaque,
};
- qemu_mutex_lock(&ctx->list_lock);
+ qemu_lockcnt_lock(&ctx->list_lock);
bh->next = ctx->first_bh;
/* Make sure that the members are ready before putting bh into list */
smp_wmb();
ctx->first_bh = bh;
- qemu_mutex_unlock(&ctx->list_lock);
+ qemu_lockcnt_unlock(&ctx->list_lock);
return bh;
}
@@ -93,13 +93,11 @@ int aio_bh_poll(AioContext *ctx)
QEMUBH *bh, **bhp, *next;
int ret;
- ctx->walking_bh++;
+ qemu_lockcnt_inc(&ctx->list_lock);
ret = 0;
- for (bh = ctx->first_bh; bh; bh = next) {
- /* Make sure that fetching bh happens before accessing its members */
- smp_read_barrier_depends();
- next = bh->next;
+ for (bh = atomic_rcu_read(&ctx->first_bh); bh; bh = next) {
+ next = atomic_rcu_read(&bh->next);
/* The atomic_xchg is paired with the one in qemu_bh_schedule. The
* implicit memory barrier ensures that the callback sees all writes
* done by the scheduling thread. It also ensures that the scheduling
@@ -116,11 +114,8 @@ int aio_bh_poll(AioContext *ctx)
}
}
- ctx->walking_bh--;
-
/* remove deleted bhs */
- if (!ctx->walking_bh) {
- qemu_mutex_lock(&ctx->list_lock);
+ if (qemu_lockcnt_dec_and_lock(&ctx->list_lock)) {
bhp = &ctx->first_bh;
while (*bhp) {
bh = *bhp;
@@ -131,7 +126,7 @@ int aio_bh_poll(AioContext *ctx)
bhp = &bh->next;
}
}
- qemu_mutex_unlock(&ctx->list_lock);
+ qemu_lockcnt_unlock(&ctx->list_lock);
}
return ret;
@@ -187,7 +182,8 @@ aio_compute_timeout(AioContext *ctx)
int timeout = -1;
QEMUBH *bh;
- for (bh = ctx->first_bh; bh; bh = bh->next) {
+ for (bh = atomic_rcu_read(&ctx->first_bh); bh;
+ bh = atomic_rcu_read(&bh->next)) {
if (bh->scheduled) {
if (bh->idle) {
/* idle bottom halves will be polled at least
@@ -270,7 +266,8 @@ aio_ctx_finalize(GSource *source)
}
#endif
- qemu_mutex_lock(&ctx->list_lock);
+ qemu_lockcnt_lock(&ctx->list_lock);
+ assert(!qemu_lockcnt_count(&ctx->list_lock));
while (ctx->first_bh) {
QEMUBH *next = ctx->first_bh->next;
@@ -280,12 +277,12 @@ aio_ctx_finalize(GSource *source)
g_free(ctx->first_bh);
ctx->first_bh = next;
}
- qemu_mutex_unlock(&ctx->list_lock);
+ qemu_lockcnt_unlock(&ctx->list_lock);
aio_set_event_notifier(ctx, &ctx->notifier, false, NULL, NULL);
event_notifier_cleanup(&ctx->notifier);
qemu_rec_mutex_destroy(&ctx->lock);
- qemu_mutex_destroy(&ctx->list_lock);
+ qemu_lockcnt_destroy(&ctx->list_lock);
timerlistgroup_deinit(&ctx->tlg);
}
@@ -372,6 +369,7 @@ AioContext *aio_context_new(Error **errp)
goto fail;
}
g_source_set_can_recurse(&ctx->source, true);
+ qemu_lockcnt_init(&ctx->list_lock);
aio_set_event_notifier(ctx, &ctx->notifier,
false,
(EventNotifierHandler *)
@@ -381,7 +379,6 @@ AioContext *aio_context_new(Error **errp)
ctx->linux_aio = NULL;
#endif
ctx->thread_pool = NULL;
- qemu_mutex_init(&ctx->list_lock);
qemu_rec_mutex_init(&ctx->lock);
timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);