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[47.55.120.4]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4ee48e86bdasm126977421cf.33.2025.11.26.11.54.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Nov 2025 11:54:13 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vOLae-000000036SQ-3jGW; Wed, 26 Nov 2025 15:54:12 -0400 Date: Wed, 26 Nov 2025 15:54:12 -0400 From: Jason Gunthorpe To: Alex Williamson Cc: kvm@vger.kernel.org, kevin.tian@intel.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] vfio/pci: Use RCU for error/request triggers to avoid circular locking Message-ID: <20251126195412.GB738503@ziepe.ca> References: <20251124223623.2770706-1-alex@shazbot.org> 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=us-ascii Content-Disposition: inline In-Reply-To: <20251124223623.2770706-1-alex@shazbot.org> On Mon, Nov 24, 2025 at 03:36:22PM -0700, Alex Williamson wrote: > From: Alex Williamson > > Thanks to a device generating an ACS violation during bus reset, > lockdep reported the following circular locking issue: > > CPU0: SET_IRQS (MSI/X): holds igate, acquires memory_lock > CPU1: HOT_RESET: holds memory_lock, acquires pci_bus_sem > CPU2: AER: holds pci_bus_sem, acquires igate > > This results in a potential 3-way deadlock. > > Remove the pci_bus_sem->igate leg of the triangle by using RCU > to peek at the eventfd rather than locking it with igate. > > Fixes: 3be3a074cf5b ("vfio-pci: Don't use device_lock around AER interrupt setup") > Signed-off-by: Alex Williamson > --- > drivers/vfio/pci/vfio_pci_core.c | 68 ++++++++++++++++++++++--------- > drivers/vfio/pci/vfio_pci_intrs.c | 52 ++++++++++++++--------- > drivers/vfio/pci/vfio_pci_priv.h | 4 ++ > include/linux/vfio_pci_core.h | 10 ++++- > 4 files changed, 93 insertions(+), 41 deletions(-) Reviewed-by: Jason Gunthorpe Jason