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authorLiu Ping Fan <qemulist@gmail.com>2013-07-16 12:28:58 +0800
committerStefan Hajnoczi <stefanha@redhat.com>2013-07-19 12:29:21 +0800
commitdcc772e2f2b7c2a68644133fea2b874f6751a57b (patch)
tree4082fc020fff1669f1e81a70fe27921e6b393e55 /async.c
parent9154b02c53bb6685797c973fcdbec51c4714777d (diff)
downloadqemu-arm-dcc772e2f2b7c2a68644133fea2b874f6751a57b.tar.gz
QEMUBH: make AioContext's bh re-entrant
BH will be used outside big lock, so introduce lock to protect between the writers, ie, bh's adders and deleter. The lock only affects the writers and bh's callback does not take this extra lock. Note that for the same AioContext, aio_bh_poll() can not run in parallel yet. Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'async.c')
-rw-r--r--async.c33
1 files changed, 31 insertions, 2 deletions
diff --git a/async.c b/async.c
index 90fe906539..5ce3633010 100644
--- a/async.c
+++ b/async.c
@@ -47,11 +47,16 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
bh->ctx = ctx;
bh->cb = cb;
bh->opaque = opaque;
+ qemu_mutex_lock(&ctx->bh_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->bh_lock);
return bh;
}
+/* Multiple occurrences of aio_bh_poll cannot be called concurrently */
int aio_bh_poll(AioContext *ctx)
{
QEMUBH *bh, **bhp, *next;
@@ -61,9 +66,15 @@ int aio_bh_poll(AioContext *ctx)
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;
if (!bh->deleted && bh->scheduled) {
bh->scheduled = 0;
+ /* Paired with write barrier in bh schedule to ensure reading for
+ * idle & callbacks coming after bh's scheduling.
+ */
+ smp_rmb();
if (!bh->idle)
ret = 1;
bh->idle = 0;
@@ -75,6 +86,7 @@ int aio_bh_poll(AioContext *ctx)
/* remove deleted bhs */
if (!ctx->walking_bh) {
+ qemu_mutex_lock(&ctx->bh_lock);
bhp = &ctx->first_bh;
while (*bhp) {
bh = *bhp;
@@ -85,6 +97,7 @@ int aio_bh_poll(AioContext *ctx)
bhp = &bh->next;
}
}
+ qemu_mutex_unlock(&ctx->bh_lock);
}
return ret;
@@ -94,24 +107,38 @@ void qemu_bh_schedule_idle(QEMUBH *bh)
{
if (bh->scheduled)
return;
- bh->scheduled = 1;
bh->idle = 1;
+ /* Make sure that idle & any writes needed by the callback are done
+ * before the locations are read in the aio_bh_poll.
+ */
+ smp_wmb();
+ bh->scheduled = 1;
}
void qemu_bh_schedule(QEMUBH *bh)
{
if (bh->scheduled)
return;
- bh->scheduled = 1;
bh->idle = 0;
+ /* Make sure that idle & any writes needed by the callback are done
+ * before the locations are read in the aio_bh_poll.
+ */
+ smp_wmb();
+ bh->scheduled = 1;
aio_notify(bh->ctx);
}
+
+/* This func is async.
+ */
void qemu_bh_cancel(QEMUBH *bh)
{
bh->scheduled = 0;
}
+/* This func is async.The bottom half will do the delete action at the finial
+ * end.
+ */
void qemu_bh_delete(QEMUBH *bh)
{
bh->scheduled = 0;
@@ -176,6 +203,7 @@ aio_ctx_finalize(GSource *source)
thread_pool_free(ctx->thread_pool);
aio_set_event_notifier(ctx, &ctx->notifier, NULL, NULL);
event_notifier_cleanup(&ctx->notifier);
+ qemu_mutex_destroy(&ctx->bh_lock);
g_array_free(ctx->pollfds, TRUE);
}
@@ -211,6 +239,7 @@ AioContext *aio_context_new(void)
ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
ctx->thread_pool = NULL;
+ qemu_mutex_init(&ctx->bh_lock);
event_notifier_init(&ctx->notifier, false);
aio_set_event_notifier(ctx, &ctx->notifier,
(EventNotifierHandler *)