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[73.222.201.58]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-241e89a3acfsm239911345ad.146.2025.08.09.19.05.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 09 Aug 2025 19:05:55 -0700 (PDT) Date: Sat, 9 Aug 2025 19:05:52 -0700 From: Joe Damato To: Jakub Kicinski Cc: davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org, willemdebruijn.kernel@gmail.com, skhawaja@google.com, sdf@fomichev.me, shuah@kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH net v2 3/3] net: prevent deadlocks when enabling NAPIs with mixed kthread config Message-ID: Mail-Followup-To: Joe Damato , Jakub Kicinski , davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org, willemdebruijn.kernel@gmail.com, skhawaja@google.com, sdf@fomichev.me, shuah@kernel.org, linux-kselftest@vger.kernel.org References: <20250809001205.1147153-1-kuba@kernel.org> <20250809001205.1147153-4-kuba@kernel.org> Precedence: bulk X-Mailing-List: netdev@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: <20250809001205.1147153-4-kuba@kernel.org> On Fri, Aug 08, 2025 at 05:12:05PM -0700, Jakub Kicinski wrote: > The following order of calls currently deadlocks if: > - device has threaded=1; and > - NAPI has persistent config with threaded=0. > > netif_napi_add_weight_config() > dev->threaded == 1 > napi_kthread_create() > > napi_enable() > napi_restore_config() > napi_set_threaded(0) > napi_stop_kthread() > while (NAPIF_STATE_SCHED) > msleep(20) > > We deadlock because disabled NAPI has STATE_SCHED set. > Creating a thread in netif_napi_add() just to destroy it in > napi_disable() is fairly ugly in the first place. Let's read > both the device config and the NAPI config in netif_napi_add(). > > Fixes: e6d76268813d ("net: Update threaded state in napi config in netif_set_threaded") > Signed-off-by: Jakub Kicinski > --- > net/core/dev.h | 8 ++++++++ > net/core/dev.c | 5 +++-- > 2 files changed, 11 insertions(+), 2 deletions(-) > Reviewed-by: Joe Damato