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Lunev" Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Kevin Wolf , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260930165000.303236-12-den@openvz.org> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 10 X-Spam_score: 1.0 X-Spam_bar: + X-Spam_report: (1.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=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-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Sep 30, 2026 at 06:49:57PM +0200, Denis V. Lunev wrote: > 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 > --- > block/blkdebug.c | 3 ++- > qemu-io-cmds.c | 5 ++--- > 2 files changed, 4 insertions(+), 4 deletions(-) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org