From ae1deee29ac316ea755c96f15b739db7a59e5c61 Mon Sep 17 00:00:00 2001

From: Kevin Wolf <kwolf@redhat.com>

Date: Wed, 10 Oct 2018 20:08:35 +0100

Subject: [PATCH 04/49] test-bdrv-drain: bdrv_drain() works with

 cross-AioContext events

RH-Author: Kevin Wolf <kwolf@redhat.com>

Message-id: <20181010200843.6710-2-kwolf@redhat.com>

Patchwork-id: 82581

O-Subject: [RHEL-8 qemu-kvm PATCH 01/44] test-bdrv-drain: bdrv_drain() works with cross-AioContext events

Bugzilla: 1637976

RH-Acked-by: Max Reitz <mreitz@redhat.com>

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

RH-Acked-by: Thomas Huth <thuth@redhat.com>

As long as nobody keeps the other I/O thread from working, there is no

reason why bdrv_drain() wouldn't work with cross-AioContext events. The

key is that the root request we're waiting for is in the AioContext

we're polling (which it always is for bdrv_drain()) so that aio_poll()

is woken up in the end.

Add a test case that shows that it works. Remove the comment in

bdrv_drain() that claims otherwise.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

(cherry picked from commit bb6756895459f181e2f25e877d3d7a10c297b5c8)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 block/io.c              |   4 --

 tests/test-bdrv-drain.c | 187 +++++++++++++++++++++++++++++++++++++++++++++++-

 2 files changed, 186 insertions(+), 5 deletions(-)

diff --git a/block/io.c b/block/io.c

index bb617de..7e0a169 100644

--- a/block/io.c

+++ b/block/io.c

@@ -369,10 +369,6 @@ void bdrv_unapply_subtree_drain(BdrvChild *child, BlockDriverState *old_parent)

  *

  * Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState

  * AioContext.

- *

- * Only this BlockDriverState's AioContext is run, so in-flight requests must

- * not depend on events in other AioContexts.  In that case, use

- * bdrv_drain_all() instead.

  */

 void coroutine_fn bdrv_co_drain(BlockDriverState *bs)

 {

diff --git a/tests/test-bdrv-drain.c b/tests/test-bdrv-drain.c

index 403446e..dee0a10 100644

--- a/tests/test-bdrv-drain.c

+++ b/tests/test-bdrv-drain.c

@@ -27,9 +27,13 @@

 #include "block/blockjob_int.h"

 #include "sysemu/block-backend.h"

 #include "qapi/error.h"

+#include "iothread.h"

+

+static QemuEvent done_event;

 typedef struct BDRVTestState {

     int drain_count;

+    AioContext *bh_indirection_ctx;

 } BDRVTestState;

 static void coroutine_fn bdrv_test_co_drain_begin(BlockDriverState *bs)

@@ -50,16 +54,29 @@ static void bdrv_test_close(BlockDriverState *bs)

     g_assert_cmpint(s->drain_count, >, 0);

 }

+static void co_reenter_bh(void *opaque)

+{

+    aio_co_wake(opaque);

+}

+

 static int coroutine_fn bdrv_test_co_preadv(BlockDriverState *bs,

                                             uint64_t offset, uint64_t bytes,

                                             QEMUIOVector *qiov, int flags)

 {

+    BDRVTestState *s = bs->opaque;

+

     /* We want this request to stay until the polling loop in drain waits for

      * it to complete. We need to sleep a while as bdrv_drain_invoke() comes

      * first and polls its result, too, but it shouldn't accidentally complete

      * this request yet. */

     qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 100000);

+    if (s->bh_indirection_ctx) {

+        aio_bh_schedule_oneshot(s->bh_indirection_ctx, co_reenter_bh,

+                                qemu_coroutine_self());

+        qemu_coroutine_yield();

+    }

+

     return 0;

 }

@@ -490,6 +507,164 @@ static void test_graph_change(void)

     blk_unref(blk_b);

 }

+struct test_iothread_data {

+    BlockDriverState *bs;

+    enum drain_type drain_type;

+    int *aio_ret;

+};

+

+static void test_iothread_drain_entry(void *opaque)

+{

+    struct test_iothread_data *data = opaque;

+

+    aio_context_acquire(bdrv_get_aio_context(data->bs));

+    do_drain_begin(data->drain_type, data->bs);

+    g_assert_cmpint(*data->aio_ret, ==, 0);

+    do_drain_end(data->drain_type, data->bs);

+    aio_context_release(bdrv_get_aio_context(data->bs));

+

+    qemu_event_set(&done_event);

+}

+

+static void test_iothread_aio_cb(void *opaque, int ret)

+{

+    int *aio_ret = opaque;

+    *aio_ret = ret;

+    qemu_event_set(&done_event);

+}

+

+/*

+ * Starts an AIO request on a BDS that runs in the AioContext of iothread 1.

+ * The request involves a BH on iothread 2 before it can complete.

+ *

+ * @drain_thread = 0 means that do_drain_begin/end are called from the main

+ * thread, @drain_thread = 1 means that they are called from iothread 1. Drain

+ * for this BDS cannot be called from iothread 2 because only the main thread

+ * may do cross-AioContext polling.

+ */

+static void test_iothread_common(enum drain_type drain_type, int drain_thread)

+{

+    BlockBackend *blk;

+    BlockDriverState *bs;

+    BDRVTestState *s;

+    BlockAIOCB *acb;

+    int aio_ret;

+    struct test_iothread_data data;

+

+    IOThread *a = iothread_new();

+    IOThread *b = iothread_new();

+    AioContext *ctx_a = iothread_get_aio_context(a);

+    AioContext *ctx_b = iothread_get_aio_context(b);

+

+    QEMUIOVector qiov;

+    struct iovec iov = {

+        .iov_base = NULL,

+        .iov_len = 0,

+    };

+    qemu_iovec_init_external(&qiov, &iov, 1);

+

+    /* bdrv_drain_all() may only be called from the main loop thread */

+    if (drain_type == BDRV_DRAIN_ALL && drain_thread != 0) {

+        goto out;

+    }

+

+    blk = blk_new(BLK_PERM_ALL, BLK_PERM_ALL);

+    bs = bdrv_new_open_driver(&bdrv_test, "test-node", BDRV_O_RDWR,

+                              &error_abort);

+    s = bs->opaque;

+    blk_insert_bs(blk, bs, &error_abort);

+

+    blk_set_aio_context(blk, ctx_a);

+    aio_context_acquire(ctx_a);

+

+    s->bh_indirection_ctx = ctx_b;

+

+    aio_ret = -EINPROGRESS;

+    if (drain_thread == 0) {

+        acb = blk_aio_preadv(blk, 0, &qiov, 0, test_iothread_aio_cb, &aio_ret);

+    } else {

+        acb = blk_aio_preadv(blk, 0, &qiov, 0, aio_ret_cb, &aio_ret);

+    }

+    g_assert(acb != NULL);

+    g_assert_cmpint(aio_ret, ==, -EINPROGRESS);

+

+    aio_context_release(ctx_a);

+

+    data = (struct test_iothread_data) {

+        .bs         = bs,

+        .drain_type = drain_type,

+        .aio_ret    = &aio_ret,

+    };

+

+    switch (drain_thread) {

+    case 0:

+        if (drain_type != BDRV_DRAIN_ALL) {

+            aio_context_acquire(ctx_a);

+        }

+

+        /* The request is running on the IOThread a. Draining its block device

+         * will make sure that it has completed as far as the BDS is concerned,

+         * but the drain in this thread can continue immediately after

+         * bdrv_dec_in_flight() and aio_ret might be assigned only slightly

+         * later. */

+        qemu_event_reset(&done_event);

+        do_drain_begin(drain_type, bs);

+        g_assert_cmpint(bs->in_flight, ==, 0);

+

+        if (drain_type != BDRV_DRAIN_ALL) {

+            aio_context_release(ctx_a);

+        }

+        qemu_event_wait(&done_event);

+        if (drain_type != BDRV_DRAIN_ALL) {

+            aio_context_acquire(ctx_a);

+        }

+

+        g_assert_cmpint(aio_ret, ==, 0);

+        do_drain_end(drain_type, bs);

+

+        if (drain_type != BDRV_DRAIN_ALL) {

+            aio_context_release(ctx_a);

+        }

+        break;

+    case 1:

+        qemu_event_reset(&done_event);

+        aio_bh_schedule_oneshot(ctx_a, test_iothread_drain_entry, &data);

+        qemu_event_wait(&done_event);

+        break;

+    default:

+        g_assert_not_reached();

+    }

+

+    aio_context_acquire(ctx_a);

+    blk_set_aio_context(blk, qemu_get_aio_context());

+    aio_context_release(ctx_a);

+

+    bdrv_unref(bs);

+    blk_unref(blk);

+

+out:

+    iothread_join(a);

+    iothread_join(b);

+}

+

+static void test_iothread_drain_all(void)

+{

+    test_iothread_common(BDRV_DRAIN_ALL, 0);

+    test_iothread_common(BDRV_DRAIN_ALL, 1);

+}

+

+static void test_iothread_drain(void)

+{

+    test_iothread_common(BDRV_DRAIN, 0);

+    test_iothread_common(BDRV_DRAIN, 1);

+}

+

+static void test_iothread_drain_subtree(void)

+{

+    test_iothread_common(BDRV_SUBTREE_DRAIN, 0);

+    test_iothread_common(BDRV_SUBTREE_DRAIN, 1);

+}

+

 typedef struct TestBlockJob {

     BlockJob common;

@@ -613,10 +788,13 @@ static void test_blockjob_drain_subtree(void)

 int main(int argc, char **argv)

 {

+    int ret;

+

     bdrv_init();

     qemu_init_main_loop(&error_abort);

     g_test_init(&argc, &argv, NULL);

+    qemu_event_init(&done_event, false);

     g_test_add_func("/bdrv-drain/driver-cb/drain_all", test_drv_cb_drain_all);

     g_test_add_func("/bdrv-drain/driver-cb/drain", test_drv_cb_drain);

@@ -643,10 +821,17 @@ int main(int argc, char **argv)

     g_test_add_func("/bdrv-drain/multiparent", test_multiparent);

     g_test_add_func("/bdrv-drain/graph-change", test_graph_change);

+    g_test_add_func("/bdrv-drain/iothread/drain_all", test_iothread_drain_all);

+    g_test_add_func("/bdrv-drain/iothread/drain", test_iothread_drain);

+    g_test_add_func("/bdrv-drain/iothread/drain_subtree",

+                    test_iothread_drain_subtree);

+

     g_test_add_func("/bdrv-drain/blockjob/drain_all", test_blockjob_drain_all);

     g_test_add_func("/bdrv-drain/blockjob/drain", test_blockjob_drain);

     g_test_add_func("/bdrv-drain/blockjob/drain_subtree",

                     test_blockjob_drain_subtree);

-    return g_test_run();

+    ret = g_test_run();

+    qemu_event_destroy(&done_event);

+    return ret;

 }

-- 

1.8.3.1