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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1718127437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ekDyI0XrbGkORk/+Y7DVMqIWcACoq55sA4lf/J9YDMA=; b=RnIB1mEXWpT7SomabiltiMKd2L5cLuvVdal/YvYqEt8tDzEA0T5Yx+AXVVGHNv7gu3V0ra UXolKcQunMBIja73cLbCr21Qcmkz2Ni8JjK2E//dlw3r2soon8yxleog8ad/Y73/cmYr08 aPwnVObMt/doI+UEru9XruWLKg5lorc= X-MC-Unique: 4Nn3CKfaPj-wGpzR5HfSNQ-1 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [PULL 3/8] aio: warn about iohandler_ctx special casing Date: Tue, 11 Jun 2024 19:36:53 +0200 Message-ID: <20240611173658.231831-4-kwolf@redhat.com> In-Reply-To: <20240611173658.231831-1-kwolf@redhat.com> References: <20240611173658.231831-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" From: Stefan Hajnoczi The main loop has two AioContexts: qemu_aio_context and iohandler_ctx. The main loop runs them both, but nested aio_poll() calls on qemu_aio_context exclude iohandler_ctx. Which one should qemu_get_current_aio_context() return when called from the main loop? Document that it's always qemu_aio_context. This has subtle effects on functions that use qemu_get_current_aio_context(). For example, aio_co_reschedule_self() does not work when moving from iohandler_ctx to qemu_aio_context because qemu_get_current_aio_context() does not differentiate these two AioContexts. Document this in order to reduce the chance of future bugs. Signed-off-by: Stefan Hajnoczi Message-ID: <20240506190622.56095-3-stefanha@redhat.com> Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- include/block/aio.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/block/aio.h b/include/block/aio.h index 8378553eb9..4ee81936ed 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -629,6 +629,9 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co); * * Move the currently running coroutine to new_ctx. If the coroutine is al= ready * running in new_ctx, do nothing. + * + * Note that this function cannot reschedule from iohandler_ctx to + * qemu_aio_context. */ void coroutine_fn aio_co_reschedule_self(AioContext *new_ctx); =20 @@ -661,6 +664,9 @@ void aio_co_enter(AioContext *ctx, Coroutine *co); * If called from an IOThread this will be the IOThread's AioContext. If * called from the main thread or with the "big QEMU lock" taken it * will be the main loop AioContext. + * + * Note that the return value is never the main loop's iohandler_ctx and t= he + * return value is the main loop AioContext instead. */ AioContext *qemu_get_current_aio_context(void); =20 --=20 2.45.2