[Qemu-devel] [PATCH] QEMUBH: make AioContext's bh re-entrant

[Liu Ping Fan <qemulist@gmail.com>]

BH will be used outside big lock, so introduce lock to protect it.
Note that the lock only affects the writer and bh's callback does
not take this extra lock.

Signed-off-by: Liu Ping Fan <pingfanl@linux.vnet.ibm.com>
---
 async.c             | 10 +++++++++-
 include/block/aio.h |  2 ++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/async.c b/async.c
index 90fe906..b1dcead 100644
--- a/async.c
+++ b/async.c
@@ -47,8 +47,11 @@ 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;
+    smp_wmb();
     ctx->first_bh = bh;
+    qemu_mutex_unlock(&ctx->bh_lock);
     return bh;
 }
 
@@ -60,7 +63,9 @@ int aio_bh_poll(AioContext *ctx)
     ctx->walking_bh++;
 
     ret = 0;
-    for (bh = ctx->first_bh; bh; bh = next) {
+    bh = ctx->first_bh;
+    smp_rmb();
+    for (; bh; bh = next) {
         next = bh->next;
         if (!bh->deleted && bh->scheduled) {
             bh->scheduled = 0;
@@ -75,6 +80,7 @@ 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 +91,7 @@ int aio_bh_poll(AioContext *ctx)
                 bhp = &bh->next;
             }
         }
+        qemu_mutex_unlock(&ctx->bh_lock);
     }
 
     return ret;
@@ -211,6 +218,7 @@ 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 *)
diff --git a/include/block/aio.h b/include/block/aio.h
index 1836793..a65d16f 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -17,6 +17,7 @@
 #include "qemu-common.h"
 #include "qemu/queue.h"
 #include "qemu/event_notifier.h"
+#include "qemu/thread.h"
 
 typedef struct BlockDriverAIOCB BlockDriverAIOCB;
 typedef void BlockDriverCompletionFunc(void *opaque, int ret);
@@ -53,6 +54,7 @@ typedef struct AioContext {
      */
     int walking_handlers;
 
+    QemuMutex bh_lock;
     /* Anchor of the list of Bottom Halves belonging to the context */
     struct QEMUBH *first_bh;
 
-- 
1.8.1.4