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[Qemu-devel] [PATCH 1/3] block: add BlockBackend->in_flight counter
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH 1/3] block: add BlockBackend->in_flight counter |
Date: |
Thu, 8 Feb 2018 17:18:05 +0000 |
BlockBackend currently relies on BlockDriverState->in_flight to track
requests for blk_drain(). There is a corner case where
BlockDriverState->in_flight cannot be used though: blk->root can be NULL
when there is no medium. This results in a segfault when the NULL
pointer is dereferenced.
Introduce a BlockBackend->in_flight counter for aio requests so it works
even when blk->root == NULL.
Based on a patch by Kevin Wolf <address@hidden>.
Signed-off-by: Kevin Wolf <address@hidden>
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
block.c | 2 +-
block/block-backend.c | 59 +++++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 53 insertions(+), 8 deletions(-)
diff --git a/block.c b/block.c
index a8da4f2b25..140f7919f8 100644
--- a/block.c
+++ b/block.c
@@ -4716,7 +4716,7 @@ out:
AioContext *bdrv_get_aio_context(BlockDriverState *bs)
{
- return bs->aio_context;
+ return bs ? bs->aio_context : qemu_get_aio_context();
}
void bdrv_coroutine_enter(BlockDriverState *bs, Coroutine *co)
diff --git a/block/block-backend.c b/block/block-backend.c
index baef8e7abc..4811d8bc55 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -71,6 +71,13 @@ struct BlockBackend {
int quiesce_counter;
VMChangeStateEntry *vmsh;
bool force_allow_inactivate;
+
+ /* Number of in-flight aio requests. BlockDriverState also counts
+ * in-flight requests but aio requests can exist even when blk->root is
+ * NULL, so we cannot rely on its counter for that case.
+ * Accessed with atomic ops.
+ */
+ unsigned int in_flight;
};
typedef struct BlockBackendAIOCB {
@@ -1223,11 +1230,21 @@ int blk_make_zero(BlockBackend *blk, BdrvRequestFlags
flags)
return bdrv_make_zero(blk->root, flags);
}
+static void blk_inc_in_flight(BlockBackend *blk)
+{
+ atomic_inc(&blk->in_flight);
+}
+
+static void blk_dec_in_flight(BlockBackend *blk)
+{
+ atomic_dec(&blk->in_flight);
+}
+
static void error_callback_bh(void *opaque)
{
struct BlockBackendAIOCB *acb = opaque;
- bdrv_dec_in_flight(acb->common.bs);
+ blk_dec_in_flight(acb->blk);
acb->common.cb(acb->common.opaque, acb->ret);
qemu_aio_unref(acb);
}
@@ -1238,7 +1255,7 @@ BlockAIOCB *blk_abort_aio_request(BlockBackend *blk,
{
struct BlockBackendAIOCB *acb;
- bdrv_inc_in_flight(blk_bs(blk));
+ blk_inc_in_flight(blk);
acb = blk_aio_get(&block_backend_aiocb_info, blk, cb, opaque);
acb->blk = blk;
acb->ret = ret;
@@ -1261,7 +1278,7 @@ static const AIOCBInfo blk_aio_em_aiocb_info = {
static void blk_aio_complete(BlkAioEmAIOCB *acb)
{
if (acb->has_returned) {
- bdrv_dec_in_flight(acb->common.bs);
+ blk_dec_in_flight(acb->rwco.blk);
acb->common.cb(acb->common.opaque, acb->rwco.ret);
qemu_aio_unref(acb);
}
@@ -1282,7 +1299,7 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk,
int64_t offset, int bytes,
BlkAioEmAIOCB *acb;
Coroutine *co;
- bdrv_inc_in_flight(blk_bs(blk));
+ blk_inc_in_flight(blk);
acb = blk_aio_get(&blk_aio_em_aiocb_info, blk, cb, opaque);
acb->rwco = (BlkRwCo) {
.blk = blk,
@@ -1519,14 +1536,42 @@ int blk_flush(BlockBackend *blk)
void blk_drain(BlockBackend *blk)
{
- if (blk_bs(blk)) {
- bdrv_drain(blk_bs(blk));
+ BlockDriverState *bs = blk_bs(blk);
+
+ if (bs) {
+ bdrv_drained_begin(bs);
+ }
+
+ /* We may have aio requests like -ENOMEDIUM in flight */
+ while (atomic_mb_read(&blk->in_flight) > 0) {
+ aio_poll(blk_get_aio_context(blk), true);
+ }
+
+ if (bs) {
+ bdrv_drained_end(bs);
}
}
void blk_drain_all(void)
{
- bdrv_drain_all();
+ BlockBackend *blk = NULL;
+
+ bdrv_drain_all_begin();
+
+ while ((blk = blk_all_next(blk)) != NULL) {
+ AioContext *ctx = blk_get_aio_context(blk);
+
+ aio_context_acquire(ctx);
+
+ /* We may have aio requests like -ENOMEDIUM in flight */
+ while (atomic_mb_read(&blk->in_flight) > 0) {
+ aio_poll(blk_get_aio_context(blk), true);
+ }
+
+ aio_context_release(ctx);
+ }
+
+ bdrv_drain_all_end();
}
void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,
--
2.14.3
Re: [Qemu-devel] [PATCH 0/3] block: fix blk_aio_*() segfault when blk->root == NULL, Eric Blake, 2018/02/09