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[47.55.120.4]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4b61ba8c52dsm10541271cf.20.2025.09.09.08.31.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Sep 2025 08:31:34 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1uw0Jh-00000003i1N-3Pgp; Tue, 09 Sep 2025 12:31:33 -0300 Date: Tue, 9 Sep 2025 12:31:33 -0300 From: Jason Gunthorpe To: Philipp Reisner Cc: Leon Romanovsky , Zhu Yanjun , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] rdma_rxe: call comp_handler without holding cq->cq_lock Message-ID: <20250909153133.GA882933@ziepe.ca> References: <20250822081941.989520-1-philipp.reisner@linbit.com> <20250908142457.GA341237@unreal> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Sep 09, 2025 at 04:48:19PM +0200, Philipp Reisner wrote: > On Mon, Sep 8, 2025 at 4:25 PM Leon Romanovsky wrote: > > > > On Fri, Aug 22, 2025 at 10:19:41AM +0200, Philipp Reisner wrote: > > > Allow the comp_handler callback implementation to call ib_poll_cq(). > > > A call to ib_poll_cq() calls rxe_poll_cq() with the rdma_rxe driver. > > > And rxe_poll_cq() locks cq->cq_lock. That leads to a spinlock deadlock. > > > > Can you please be more specific about the deadlock? > > Please write call stack to describe it. > > > Instead of a call stack, I write it from top to bottom: > > The line numbers in the .c files are valid for Linux-6.16: > > 1 rxe_cq_post() [rxe_cq.c:85] > 2 spin_lock_irqsave() [rxe_cq.c:93] > 3 cq->ibcq.comp_handler() [rxe_cq.c:116] > 4 some_comp_handler() > 5 ib_poll_cq() > 6 cq->device->ops.poll_cq() [ib_verbs.h:4037] > 7 rxe_poll_cq() [rxe_verbs.c:1165] > 8 spin_lock_irqsave() [rxe_verbs.c:1172] > > In line 8 of this call graph, it deadlocks because the spinlock > was already acquired in line 2 of the call graph. Is this even legal in verbs? I'm not sure you can do pull cq from a interrupt driven comp handler.. Is something already doing this intree? Jason