From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: qemu-block@nongnu.org
Cc: qemu-devel@nongnu.org, fam@euphon.net, stefanha@redhat.com,
mreitz@redhat.com, kwolf@redhat.com, vsementsov@virtuozzo.com,
eblake@redhat.com, rvkagan@yandex-team.ru
Subject: [PATCH v2 03/10] util/async: aio_co_enter(): do aio_co_schedule in general case
Date: Thu, 8 Apr 2021 17:08:20 +0300 [thread overview]
Message-ID: <20210408140827.332915-4-vsementsov@virtuozzo.com> (raw)
In-Reply-To: <20210408140827.332915-1-vsementsov@virtuozzo.com>
With the following patch we want to call aio_co_wake() from thread.
And it works bad.
Assume we have no iothreads.
Assume we have a coroutine A, which waits in the yield point for external
aio_co_wake(), and no progress can be done until it happen.
Main thread is in blocking aio_poll() (for example, in blk_read()).
Now, in a separate thread we do aio_co_wake(). It calls aio_co_enter(),
which goes through last "else" branch and do aio_context_acquire(ctx).
Now we have a deadlock, as aio_poll() will not release the context lock
until some progress is done, and progress can't be done until
aio_co_wake() wake the coroutine A. And it can't because it wait for
aio_context_acquire().
Still, aio_co_schedule() works well in parallel with blocking
aio_poll(). So let's use it in generic case and drop
aio_context_acquire/aio_context_release branch from aio_co_enter().
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
util/async.c | 11 ++---------
1 file changed, 2 insertions(+), 9 deletions(-)
diff --git a/util/async.c b/util/async.c
index 674dbefb7c..f05b883a39 100644
--- a/util/async.c
+++ b/util/async.c
@@ -614,19 +614,12 @@ void aio_co_wake(struct Coroutine *co)
void aio_co_enter(AioContext *ctx, struct Coroutine *co)
{
- if (ctx != qemu_get_current_aio_context()) {
- aio_co_schedule(ctx, co);
- return;
- }
-
- if (qemu_in_coroutine()) {
+ if (ctx == qemu_get_current_aio_context() && qemu_in_coroutine()) {
Coroutine *self = qemu_coroutine_self();
assert(self != co);
QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
} else {
- aio_context_acquire(ctx);
- qemu_aio_coroutine_enter(ctx, co);
- aio_context_release(ctx);
+ aio_co_schedule(ctx, co);
}
}
--
2.29.2
next prev parent reply other threads:[~2021-04-08 14:24 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 14:08 [PATCH v2 00/10] block/nbd: move connection code to separate file Vladimir Sementsov-Ogievskiy
2021-04-08 14:08 ` [PATCH v2 01/10] block/nbd: introduce NBDConnectThread reference counter Vladimir Sementsov-Ogievskiy
2021-04-08 15:31 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 02/10] block/nbd: BDRVNBDState: drop unused connect_err and connect_status Vladimir Sementsov-Ogievskiy
2021-04-08 15:33 ` Roman Kagan
2021-04-08 14:08 ` Vladimir Sementsov-Ogievskiy [this message]
2021-04-08 15:54 ` [PATCH v2 03/10] util/async: aio_co_enter(): do aio_co_schedule in general case Roman Kagan
2021-04-09 14:38 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 04/10] block/nbd: simplify waking of nbd_co_establish_connection() Vladimir Sementsov-Ogievskiy
2021-04-08 16:10 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 05/10] block/nbd: drop thr->state Vladimir Sementsov-Ogievskiy
2021-04-08 16:36 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 06/10] block/nbd: bs-independent interface for nbd_co_establish_connection() Vladimir Sementsov-Ogievskiy
2021-04-08 16:45 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 07/10] block/nbd: make nbd_co_establish_connection_cancel() bs-independent Vladimir Sementsov-Ogievskiy
2021-04-08 16:50 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 08/10] block/nbd: rename NBDConnectThread to NBDClientConnection Vladimir Sementsov-Ogievskiy
2021-04-08 16:54 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 09/10] block/nbd: introduce nbd_client_connection_new() Vladimir Sementsov-Ogievskiy
2021-04-08 16:57 ` Roman Kagan
2021-04-08 14:08 ` [PATCH v2 10/10] nbd: move connection code from block/nbd to nbd/client-connection Vladimir Sementsov-Ogievskiy
2021-04-08 17:04 ` Roman Kagan
2021-04-08 17:07 ` Vladimir Sementsov-Ogievskiy
2021-06-02 21:32 ` Eric Blake
2021-04-08 17:16 ` [PATCH v2 00/10] block/nbd: move connection code to separate file Roman Kagan
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