From ab88ad152dbdf6e906da07e2c165f01985edfe13 Mon Sep 17 00:00:00 2001

From: Jeffrey Cody <jcody@redhat.com>

Date: Thu, 30 Nov 2017 22:49:08 +0100

Subject: [PATCH 04/21] coroutine: abort if we try to schedule or enter a

 pending coroutine

RH-Author: Jeffrey Cody <jcody@redhat.com>

Message-id: <27811c58f7dd73e9d8b6f51aff42a7de9bae37fc.1511985875.git.jcody@redhat.com>

Patchwork-id: 78044

O-Subject: [RHV7.5 qemu-kvm-rhev PATCH 04/11] coroutine: abort if we try to schedule or enter a pending coroutine

Bugzilla: 1506531

RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

RH-Acked-by: John Snow <jsnow@redhat.com>

The previous patch fixed a race condition, in which there were

coroutines being executing doubly, or after coroutine deletion.

We can detect common scenarios when this happens, and print an error

message and abort before we corrupt memory / data, or segfault.

This patch will abort if an attempt to enter a coroutine is made while

it is currently pending execution, either in a specific AioContext bh,

or pending execution via a timer.  It will also abort if a coroutine

is scheduled, before a prior scheduled run has occurred.

We cannot rely on the existing co->caller check for recursive re-entry

to catch this, as the coroutine may run and exit with

COROUTINE_TERMINATE before the scheduled coroutine executes.

(This is the scenario that was occurring and fixed in the previous

patch).

This patch also re-orders the Coroutine struct elements in an attempt to

optimize caching.

Signed-off-by: Jeff Cody <jcody@redhat.com>

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

(cherry picked from commit 6133b39f3c36623425a6ede9e89d93175fde15cd)

Signed-off-by: Jeff Cody <jcody@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 include/qemu/coroutine_int.h | 13 ++++++++++---

 util/async.c                 | 13 +++++++++++++

 util/qemu-coroutine-sleep.c  | 12 ++++++++++++

 util/qemu-coroutine.c        | 14 ++++++++++++++

 4 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/include/qemu/coroutine_int.h b/include/qemu/coroutine_int.h

index cb98892..59e8406 100644

--- a/include/qemu/coroutine_int.h

+++ b/include/qemu/coroutine_int.h

@@ -46,14 +46,21 @@ struct Coroutine {

     size_t locks_held;

+    /* Only used when the coroutine has yielded.  */

+    AioContext *ctx;

+

+    /* Used to catch and abort on illegal co-routine entry.

+     * Will contain the name of the function that had first

+     * scheduled the coroutine. */

+    const char *scheduled;

+

+    QSIMPLEQ_ENTRY(Coroutine) co_queue_next;

+

     /* Coroutines that should be woken up when we yield or terminate.

      * Only used when the coroutine is running.

      */

     QSIMPLEQ_HEAD(, Coroutine) co_queue_wakeup;

-    /* Only used when the coroutine has yielded.  */

-    AioContext *ctx;

-    QSIMPLEQ_ENTRY(Coroutine) co_queue_next;

     QSLIST_ENTRY(Coroutine) co_scheduled_next;

 };

diff --git a/util/async.c b/util/async.c

index 0e1bd87..4dd9d95 100644

--- a/util/async.c

+++ b/util/async.c

@@ -388,6 +388,9 @@ static void co_schedule_bh_cb(void *opaque)

         QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);

         trace_aio_co_schedule_bh_cb(ctx, co);

         aio_context_acquire(ctx);

+

+        /* Protected by write barrier in qemu_aio_coroutine_enter */

+        atomic_set(&co->scheduled, NULL);

         qemu_coroutine_enter(co);

         aio_context_release(ctx);

     }

@@ -438,6 +441,16 @@ fail:

 void aio_co_schedule(AioContext *ctx, Coroutine *co)

 {

     trace_aio_co_schedule(ctx, co);

+    const char *scheduled = atomic_cmpxchg(&co->scheduled, NULL,

+                                           __func__);

+

+    if (scheduled) {

+        fprintf(stderr,

+                "%s: Co-routine was already scheduled in '%s'\n",

+                __func__, scheduled);

+        abort();

+    }

+

     QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines,

                               co, co_scheduled_next);

     qemu_bh_schedule(ctx->co_schedule_bh);

diff --git a/util/qemu-coroutine-sleep.c b/util/qemu-coroutine-sleep.c

index 9c56550..254349c 100644

--- a/util/qemu-coroutine-sleep.c

+++ b/util/qemu-coroutine-sleep.c

@@ -13,6 +13,7 @@

 #include "qemu/osdep.h"

 #include "qemu/coroutine.h"

+#include "qemu/coroutine_int.h"

 #include "qemu/timer.h"

 #include "block/aio.h"

@@ -25,6 +26,8 @@ static void co_sleep_cb(void *opaque)

 {

     CoSleepCB *sleep_cb = opaque;

+    /* Write of schedule protected by barrier write in aio_co_schedule */

+    atomic_set(&sleep_cb->co->scheduled, NULL);

     aio_co_wake(sleep_cb->co);

 }

@@ -34,6 +37,15 @@ void coroutine_fn co_aio_sleep_ns(AioContext *ctx, QEMUClockType type,

     CoSleepCB sleep_cb = {

         .co = qemu_coroutine_self(),

     };

+

+    const char *scheduled = atomic_cmpxchg(&sleep_cb.co->scheduled, NULL,

+                                           __func__);

+    if (scheduled) {

+        fprintf(stderr,

+                "%s: Co-routine was already scheduled in '%s'\n",

+                __func__, scheduled);

+        abort();

+    }

     sleep_cb.ts = aio_timer_new(ctx, type, SCALE_NS, co_sleep_cb, &sleep_cb);

     timer_mod(sleep_cb.ts, qemu_clock_get_ns(type) + ns);

     qemu_coroutine_yield();

diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c

index d6095c1..9eff7fd 100644

--- a/util/qemu-coroutine.c

+++ b/util/qemu-coroutine.c

@@ -107,8 +107,22 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co)

     Coroutine *self = qemu_coroutine_self();

     CoroutineAction ret;

+    /* Cannot rely on the read barrier for co in aio_co_wake(), as there are

+     * callers outside of aio_co_wake() */

+    const char *scheduled = atomic_mb_read(&co->scheduled);

+

     trace_qemu_aio_coroutine_enter(ctx, self, co, co->entry_arg);

+    /* if the Coroutine has already been scheduled, entering it again will

+     * cause us to enter it twice, potentially even after the coroutine has

+     * been deleted */

+    if (scheduled) {

+        fprintf(stderr,

+                "%s: Co-routine was already scheduled in '%s'\n",

+                __func__, scheduled);

+        abort();

+    }

+

     if (co->caller) {

         fprintf(stderr, "Co-routine re-entered recursively\n");

         abort();

-- 

1.8.3.1