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Lunev" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Hanna Reitz , Vladimir Sementsov-Ogievskiy , Andrey Drobyshev Subject: Re: [PATCH 11/13] block/blkdebug: make a breakpoint work across AioContexts Message-ID: References: <20260930165000.303236-1-den@openvz.org> <20260930165000.303236-12-den@openvz.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260930165000.303236-12-den@openvz.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 5 X-Spam_score: 0.5 X-Spam_bar: / X-Spam_report: (0.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Am 30.09.2026 um 18:49 hat Denis V. Lunev geschrieben: > From: Denis V. Lunev > > A request that stops at a breakpoint belongs to whichever AioContext > issued it, and the monitor or qemu-io that resumes it runs somewhere > else. Two things go wrong once those are not the same thread. > > resume_req_by_tag() woke the request with qemu_coroutine_enter(), which > enters the coroutine on the caller's thread. That moves the request off > its own thread for the rest of its life, and it aborts outright when it > wins the race against the yield, because the request is published to > the list before the coroutine gets there. > > wait_break polled the block backend's AioContext, where the event will > never arrive, so it slept through the suspension it was waiting for. > > Wake the request in the context it came from and wait for it the way > the rest of the block layer waits across contexts. Where the two > contexts are the same the coroutine is still entered directly, so > single-threaded behaviour, and the output tests depending on it, do not > change. > > Signed-off-by: Denis V. Lunev > CC: Kevin Wolf > CC: Hanna Reitz > CC: Vladimir Sementsov-Ogievskiy > CC: Andrey Drobyshev Maybe order this one before the patch that lets qemu-io start requests in iothreads? In practice, this is what exposes the problem. (Though yes, theoretically you could provoke it in other ways, too.) > block/blkdebug.c | 3 ++- > qemu-io-cmds.c | 5 ++--- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/block/blkdebug.c b/block/blkdebug.c > index 78cc03746f..1522015b34 100644 > --- a/block/blkdebug.c > +++ b/block/blkdebug.c > @@ -813,6 +813,7 @@ static void suspend_request(BlockDriverState *bs, BlkdebugRule *rule) > > remove_rule(rule); > QLIST_INSERT_HEAD(&s->suspended_reqs, r, next); > + aio_wait_kick(); Could this use a comment to tell that this wakes up the 'wait_break' command in qemu-io? Kevin