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From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-devel@nongnu.org
Cc: qemu-block@nongnu.org, eesposit@redhat.com, kwolf@redhat.com
Subject: [PATCH 07/15] block-backend: enter aio coroutine only after drain
Date: Mon, 12 Dec 2022 13:59:12 +0100	[thread overview]
Message-ID: <20221212125920.248567-8-pbonzini@redhat.com> (raw)
In-Reply-To: <20221212125920.248567-1-pbonzini@redhat.com>

When called from within (another) coroutine, aio_co_enter will not
enter a coroutine immediately; instead the new coroutine is scheduled
to run after qemu_coroutine_yield().  This however might cause the
currently-running coroutine to yield without having raised blk->in_flight.
If it was a ->drained_begin() callback who scheduled the coroutine,
bdrv_drained_begin() might exit without waiting for the I/O operation
to finish.  Right now, this is masked by unnecessary polling done by
bdrv_drained_begin() after the callbacks return, but it is wrong and
a latent bug.

So, ensure that blk_inc_in_flight() and blk_wait_while_drained()
are called before aio_co_enter().  To do so, pull the call to
blk_wait_while_drained() out of the blk_co_do_* functions, which are
called from the AIO coroutines, and place them separately in the public
blk_co_* functions and in blk_aio_prwv.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/block-backend.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 2852a892de6c..c4a884b86c2b 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1288,8 +1288,6 @@ blk_co_do_preadv_part(BlockBackend *blk, int64_t offset, int64_t bytes,
     BlockDriverState *bs;
     IO_CODE();
 
-    blk_wait_while_drained(blk);
-
     /* Call blk_bs() only after waiting, the graph may have changed */
     bs = blk_bs(blk);
     trace_blk_co_preadv(blk, bs, offset, bytes, flags);
@@ -1332,6 +1330,7 @@ int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
     IO_OR_GS_CODE();
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     ret = blk_co_do_preadv_part(blk, offset, bytes, qiov, 0, flags);
     blk_dec_in_flight(blk);
 
@@ -1346,6 +1345,7 @@ int coroutine_fn blk_co_preadv_part(BlockBackend *blk, int64_t offset,
     IO_OR_GS_CODE();
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     ret = blk_co_do_preadv_part(blk, offset, bytes, qiov, qiov_offset, flags);
     blk_dec_in_flight(blk);
 
@@ -1362,8 +1362,6 @@ blk_co_do_pwritev_part(BlockBackend *blk, int64_t offset, int64_t bytes,
     BlockDriverState *bs;
     IO_CODE();
 
-    blk_wait_while_drained(blk);
-
     /* Call blk_bs() only after waiting, the graph may have changed */
     bs = blk_bs(blk);
     trace_blk_co_pwritev(blk, bs, offset, bytes, flags);
@@ -1399,6 +1397,7 @@ int coroutine_fn blk_co_pwritev_part(BlockBackend *blk, int64_t offset,
     IO_OR_GS_CODE();
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     ret = blk_co_do_pwritev_part(blk, offset, bytes, qiov, qiov_offset, flags);
     blk_dec_in_flight(blk);
 
@@ -1543,6 +1542,7 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset,
     Coroutine *co;
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     acb = blk_aio_get(&blk_aio_em_aiocb_info, blk, cb, opaque);
     acb->rwco = (BlkRwCo) {
         .blk    = blk,
@@ -1667,8 +1667,6 @@ blk_co_do_ioctl(BlockBackend *blk, unsigned long int req, void *buf)
 {
     IO_CODE();
 
-    blk_wait_while_drained(blk);
-
     if (!blk_is_available(blk)) {
         return -ENOMEDIUM;
     }
@@ -1683,6 +1681,7 @@ int coroutine_fn blk_co_ioctl(BlockBackend *blk, unsigned long int req,
     IO_OR_GS_CODE();
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     ret = blk_co_do_ioctl(blk, req, buf);
     blk_dec_in_flight(blk);
 
@@ -1713,8 +1712,6 @@ blk_co_do_pdiscard(BlockBackend *blk, int64_t offset, int64_t bytes)
     int ret;
     IO_CODE();
 
-    blk_wait_while_drained(blk);
-
     ret = blk_check_byte_request(blk, offset, bytes);
     if (ret < 0) {
         return ret;
@@ -1748,6 +1745,7 @@ int coroutine_fn blk_co_pdiscard(BlockBackend *blk, int64_t offset,
     IO_OR_GS_CODE();
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     ret = blk_co_do_pdiscard(blk, offset, bytes);
     blk_dec_in_flight(blk);
 
@@ -1757,7 +1755,6 @@ int coroutine_fn blk_co_pdiscard(BlockBackend *blk, int64_t offset,
 /* To be called between exactly one pair of blk_inc/dec_in_flight() */
 static int coroutine_fn blk_co_do_flush(BlockBackend *blk)
 {
-    blk_wait_while_drained(blk);
     IO_CODE();
 
     if (!blk_is_available(blk)) {
@@ -1789,6 +1786,7 @@ int coroutine_fn blk_co_flush(BlockBackend *blk)
     IO_OR_GS_CODE();
 
     blk_inc_in_flight(blk);
+    blk_wait_while_drained(blk);
     ret = blk_co_do_flush(blk);
     blk_dec_in_flight(blk);
 
-- 
2.38.1



  parent reply	other threads:[~2022-12-12 13:08 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-12-12 12:59 [PATCH 00/12] More cleanups and fixes for drain Paolo Bonzini
2022-12-12 12:59 ` [PATCH 01/15] Revert "block: Remove poll parameter from bdrv_parent_drained_begin_single()" Paolo Bonzini
2022-12-12 12:59 ` [PATCH 02/15] Revert "block: Don't poll in bdrv_replace_child_noperm()" Paolo Bonzini
2022-12-12 12:59 ` [PATCH 03/15] block: Pull polling out of bdrv_parent_drained_begin_single() Paolo Bonzini
2022-12-12 12:59 ` [PATCH 04/15] test-bdrv-drain.c: remove test_detach_by_parent_cb() Paolo Bonzini
2022-12-12 12:59 ` [PATCH 05/15] tests/unit/test-bdrv-drain.c: graph setup functions can't run in coroutines Paolo Bonzini
2022-12-12 12:59 ` [PATCH 06/15] tests/qemu-iotests/030: test_stream_parallel should use auto_finalize=False Paolo Bonzini
2022-12-12 12:59 ` Paolo Bonzini [this message]
2023-01-16 15:57   ` [PATCH 07/15] block-backend: enter aio coroutine only after drain Kevin Wolf
2022-12-12 12:59 ` [PATCH 08/15] nbd: a BlockExport always has a BlockBackend Paolo Bonzini
2022-12-12 12:59 ` [PATCH 09/15] block-backend: make global properties write-once Paolo Bonzini
2022-12-12 12:59 ` [PATCH 10/15] block-backend: always wait for drain before starting operation Paolo Bonzini
2023-01-16 16:48   ` Kevin Wolf
2022-12-12 12:59 ` [PATCH 11/15] block-backend: make queued_requests thread-safe Paolo Bonzini
2023-01-11 20:44   ` Stefan Hajnoczi
2023-01-16 16:55   ` Kevin Wolf
2022-12-12 12:59 ` [PATCH 12/15] block: limit bdrv_co_yield_to_drain to drain_begin Paolo Bonzini
2022-12-12 12:59 ` [PATCH 13/15] block: second argument of bdrv_do_drained_end is always NULL Paolo Bonzini
2022-12-12 12:59 ` [PATCH 14/15] block: second argument of bdrv_do_drained_begin and bdrv_drain_poll " Paolo Bonzini
2022-12-12 12:59 ` [PATCH 15/15] block: only get out of coroutine context for polling Paolo Bonzini
2023-01-16 15:51 ` [PATCH 00/12] More cleanups and fixes for drain Kevin Wolf
2023-01-16 17:25 ` Kevin Wolf

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