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[Qemu-block] [PATCH 06/14] block: Add missing locking in bdrv_co_drain_b
From: |
Kevin Wolf |
Subject: |
[Qemu-block] [PATCH 06/14] block: Add missing locking in bdrv_co_drain_bh_cb() |
Date: |
Fri, 7 Sep 2018 18:15:12 +0200 |
bdrv_do_drained_begin/end() assume that they are called with the
AioContext lock of bs held. If we call drain functions from a coroutine
with the AioContext lock held, we yield and schedule a BH to move out of
coroutine context. This means that the lock for the home context of the
coroutine is released and must be re-acquired in the bottom half.
Signed-off-by: Kevin Wolf <address@hidden>
---
include/qemu/coroutine.h | 5 +++++
block/io.c | 15 +++++++++++++++
util/qemu-coroutine.c | 5 +++++
3 files changed, 25 insertions(+)
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index 6f8a487041..9801e7f5a4 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -90,6 +90,11 @@ void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine
*co);
void coroutine_fn qemu_coroutine_yield(void);
/**
+ * Get the AioContext of the given coroutine
+ */
+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co);
+
+/**
* Get the currently executing coroutine
*/
Coroutine *coroutine_fn qemu_coroutine_self(void);
diff --git a/block/io.c b/block/io.c
index 7100344c7b..914ba78f1a 100644
--- a/block/io.c
+++ b/block/io.c
@@ -288,6 +288,18 @@ static void bdrv_co_drain_bh_cb(void *opaque)
BlockDriverState *bs = data->bs;
if (bs) {
+ AioContext *ctx = bdrv_get_aio_context(bs);
+ AioContext *co_ctx = qemu_coroutine_get_aio_context(co);
+
+ /*
+ * When the coroutine yielded, the lock for its home context was
+ * released, so we need to re-acquire it here. If it explicitly
+ * acquired a different context, the lock is still held and we don't
+ * want to lock it a second time (or AIO_WAIT_WHILE() would hang).
+ */
+ if (ctx == co_ctx) {
+ aio_context_acquire(ctx);
+ }
bdrv_dec_in_flight(bs);
if (data->begin) {
bdrv_do_drained_begin(bs, data->recursive, data->parent,
@@ -296,6 +308,9 @@ static void bdrv_co_drain_bh_cb(void *opaque)
bdrv_do_drained_end(bs, data->recursive, data->parent,
data->ignore_bds_parents);
}
+ if (ctx == co_ctx) {
+ aio_context_release(ctx);
+ }
} else {
assert(data->begin);
bdrv_drain_all_begin();
diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c
index 1ba4191b84..2295928d33 100644
--- a/util/qemu-coroutine.c
+++ b/util/qemu-coroutine.c
@@ -198,3 +198,8 @@ bool qemu_coroutine_entered(Coroutine *co)
{
return co->caller;
}
+
+AioContext *coroutine_fn qemu_coroutine_get_aio_context(Coroutine *co)
+{
+ return co->ctx;
+}
--
2.13.6
- [Qemu-block] [PATCH 01/14] blockjob: Wake up BDS when job becomes idle, (continued)
- [Qemu-block] [PATCH 01/14] blockjob: Wake up BDS when job becomes idle, Kevin Wolf, 2018/09/07
- [Qemu-block] [PATCH 04/14] job: Use AIO_WAIT_WHILE() in job_finish_sync(), Kevin Wolf, 2018/09/07
- [Qemu-block] [PATCH 02/14] test-bdrv-drain: Drain with block jobs in an I/O thread, Kevin Wolf, 2018/09/07
- [Qemu-block] [PATCH 07/14] aio-wait: Increase num_waiters even in home thread, Kevin Wolf, 2018/09/07
- [Qemu-block] [PATCH 05/14] test-bdrv-drain: Test AIO_WAIT_WHILE() in completion callback, Kevin Wolf, 2018/09/07
- [Qemu-block] [PATCH 06/14] block: Add missing locking in bdrv_co_drain_bh_cb(),
Kevin Wolf <=
[Qemu-block] [PATCH 08/14] block-backend: Add .drained_poll callback, Kevin Wolf, 2018/09/07
[Qemu-block] [PATCH 09/14] block-backend: Fix potential double blk_delete(), Kevin Wolf, 2018/09/07
[Qemu-block] [PATCH 12/14] blockjob: Lie better in child_job_drained_poll(), Kevin Wolf, 2018/09/07