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From 0bf037188149824a8ae161ad9dea7d650b6f7346 Mon Sep 17 00:00:00 2001
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From: Gerd Hoffmann <kraxel@redhat.com>
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Date: Tue, 21 Jan 2014 11:25:16 -0500
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Subject: [PATCH 5/6] QEMUBH: make AioContext's bh re-entrant
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Message-id: <1390303517-20167-2-git-send-email-kraxel@redhat.com>
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Patchwork-id: 56866
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O-Subject: [RHEL-7 qemu-kvm PATCH 1/2] QEMUBH: make AioContext's bh re-entrant
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Bugzilla: 1009297
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
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From: Liu Ping Fan <qemulist@gmail.com>
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BH will be used outside big lock, so introduce lock to protect
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between the writers, ie, bh's adders and deleter. The lock only
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affects the writers and bh's callback does not take this extra lock.
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Note that for the same AioContext, aio_bh_poll() can not run in
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parallel yet.
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Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit dcc772e2f2b7c2a68644133fea2b874f6751a57b)
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---
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 async.c             | 33 +++++++++++++++++++++++++++++++--
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 include/block/aio.h |  7 +++++++
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 2 files changed, 38 insertions(+), 2 deletions(-)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 async.c             | 33 +++++++++++++++++++++++++++++++--
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 include/block/aio.h |  7 +++++++
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 2 files changed, 38 insertions(+), 2 deletions(-)
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diff --git a/async.c b/async.c
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index 90fe906..5ce3633 100644
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--- a/async.c
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+++ b/async.c
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@@ -47,11 +47,16 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
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     bh->ctx = ctx;
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     bh->cb = cb;
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     bh->opaque = opaque;
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+    qemu_mutex_lock(&ctx->bh_lock);
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     bh->next = ctx->first_bh;
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+    /* Make sure that the members are ready before putting bh into list */
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+    smp_wmb();
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     ctx->first_bh = bh;
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+    qemu_mutex_unlock(&ctx->bh_lock);
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     return bh;
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 }
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+/* Multiple occurrences of aio_bh_poll cannot be called concurrently */
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 int aio_bh_poll(AioContext *ctx)
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 {
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     QEMUBH *bh, **bhp, *next;
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@@ -61,9 +66,15 @@ int aio_bh_poll(AioContext *ctx)
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     ret = 0;
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     for (bh = ctx->first_bh; bh; bh = next) {
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+        /* Make sure that fetching bh happens before accessing its members */
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+        smp_read_barrier_depends();
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         next = bh->next;
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         if (!bh->deleted && bh->scheduled) {
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             bh->scheduled = 0;
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+            /* Paired with write barrier in bh schedule to ensure reading for
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+             * idle & callbacks coming after bh's scheduling.
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+             */
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+            smp_rmb();
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             if (!bh->idle)
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                 ret = 1;
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             bh->idle = 0;
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@@ -75,6 +86,7 @@ int aio_bh_poll(AioContext *ctx)
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     /* remove deleted bhs */
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     if (!ctx->walking_bh) {
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+        qemu_mutex_lock(&ctx->bh_lock);
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         bhp = &ctx->first_bh;
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         while (*bhp) {
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             bh = *bhp;
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@@ -85,6 +97,7 @@ int aio_bh_poll(AioContext *ctx)
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                 bhp = &bh->next;
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             }
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         }
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+        qemu_mutex_unlock(&ctx->bh_lock);
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     }
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     return ret;
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@@ -94,24 +107,38 @@ void qemu_bh_schedule_idle(QEMUBH *bh)
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 {
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     if (bh->scheduled)
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         return;
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-    bh->scheduled = 1;
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     bh->idle = 1;
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+    /* Make sure that idle & any writes needed by the callback are done
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+     * before the locations are read in the aio_bh_poll.
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+     */
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+    smp_wmb();
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+    bh->scheduled = 1;
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 }
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 void qemu_bh_schedule(QEMUBH *bh)
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 {
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     if (bh->scheduled)
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         return;
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-    bh->scheduled = 1;
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     bh->idle = 0;
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+    /* Make sure that idle & any writes needed by the callback are done
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+     * before the locations are read in the aio_bh_poll.
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+     */
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+    smp_wmb();
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+    bh->scheduled = 1;
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     aio_notify(bh->ctx);
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 }
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+
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+/* This func is async.
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+ */
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 void qemu_bh_cancel(QEMUBH *bh)
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 {
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     bh->scheduled = 0;
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 }
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+/* This func is async.The bottom half will do the delete action at the finial
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+ * end.
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+ */
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 void qemu_bh_delete(QEMUBH *bh)
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 {
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     bh->scheduled = 0;
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@@ -176,6 +203,7 @@ aio_ctx_finalize(GSource     *source)
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     thread_pool_free(ctx->thread_pool);
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     aio_set_event_notifier(ctx, &ctx->notifier, NULL, NULL);
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     event_notifier_cleanup(&ctx->notifier);
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+    qemu_mutex_destroy(&ctx->bh_lock);
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     g_array_free(ctx->pollfds, TRUE);
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 }
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@@ -211,6 +239,7 @@ AioContext *aio_context_new(void)
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     ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
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     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
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     ctx->thread_pool = NULL;
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+    qemu_mutex_init(&ctx->bh_lock);
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     event_notifier_init(&ctx->notifier, false);
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     aio_set_event_notifier(ctx, &ctx->notifier, 
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                            (EventNotifierHandler *)
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diff --git a/include/block/aio.h b/include/block/aio.h
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index 1836793..cc77771 100644
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--- a/include/block/aio.h
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+++ b/include/block/aio.h
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@@ -17,6 +17,7 @@
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 #include "qemu-common.h"
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 #include "qemu/queue.h"
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 #include "qemu/event_notifier.h"
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+#include "qemu/thread.h"
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 typedef struct BlockDriverAIOCB BlockDriverAIOCB;
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 typedef void BlockDriverCompletionFunc(void *opaque, int ret);
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@@ -53,6 +54,8 @@ typedef struct AioContext {
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      */
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     int walking_handlers;
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+    /* lock to protect between bh's adders and deleter */
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+    QemuMutex bh_lock;
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     /* Anchor of the list of Bottom Halves belonging to the context */
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     struct QEMUBH *first_bh;
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@@ -127,6 +130,8 @@ void aio_notify(AioContext *ctx);
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  * aio_bh_poll: Poll bottom halves for an AioContext.
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  *
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  * These are internal functions used by the QEMU main loop.
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+ * And notice that multiple occurrences of aio_bh_poll cannot
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+ * be called concurrently
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  */
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 int aio_bh_poll(AioContext *ctx);
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@@ -163,6 +168,8 @@ void qemu_bh_cancel(QEMUBH *bh);
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  * Deleting a bottom half frees the memory that was allocated for it by
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  * qemu_bh_new.  It also implies canceling the bottom half if it was
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  * scheduled.
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+ * This func is async. The bottom half will do the delete action at the finial
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+ * end.
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  *
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  * @bh: The bottom half to be deleted.
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  */
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-- 
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1.8.3.1
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