On Sat, Jun 15, 2013 at 1:35 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> Il 13/06/2013 22:55, Liu Ping Fan ha scritto:
>> 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 <pingf...@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;
>
> The read barrier in theory should go inside the loop. On the other
For read after more than 1 writer?
> hand, it only needs to be a smp_read_barrier_depends().
>
Ok, so it will depend on ops introduced in your urcu patch series.
Thanks and regards,
Pingfan
> Paolo
>
>> 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;
>>
>>
>
