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[73.158.218.242]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-237d867b438sm141528705ad.176.2025.06.25.16.37.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Jun 2025 16:37:44 -0700 (PDT) Date: Wed, 25 Jun 2025 16:37:43 -0700 From: Stanislav Fomichev To: Jakub Kicinski Cc: Jason Xing , syzbot , andrii@kernel.org, ast@kernel.org, bjorn@kernel.org, bpf@vger.kernel.org, daniel@iogearbox.net, davem@davemloft.net, edumazet@google.com, horms@kernel.org, jonathan.lemon@gmail.com, linux-kernel@vger.kernel.org, maciej.fijalkowski@intel.com, magnus.karlsson@intel.com, netdev@vger.kernel.org, pabeni@redhat.com, sdf@fomichev.me, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [bpf?] [net?] possible deadlock in xsk_notifier (3) Message-ID: References: <685af3b1.a00a0220.2e5631.0091.GAE@google.com> <20250625140357.6203d0af@kernel.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=utf-8 Content-Disposition: inline In-Reply-To: <20250625140357.6203d0af@kernel.org> On 06/25, Jakub Kicinski wrote: > On Wed, 25 Jun 2025 13:48:03 -0700 Stanislav Fomichev wrote: > > > > I'm still learning the af_xdp. Sure, I'm interested in it, just a bit > > > > worried if I'm capable of completing it. I will try then. > > > > > > SG, thanks! If you need more details lmk, but basically we need to reorder > > > netdev_lock_ops() and mutex_lock(lock: &xs->mutex)+XSK_READY check. > > > And similarly for cleanup (out_unlock/out_release) path. > > > > Jakub just told me that I'm wrong and it looks similar to commit > > f0433eea4688 ("net: don't mix device locking in dev_close_many() > > calls"). So this is not as easy as flipping the lock ordering :-( > > I don't think registering a netdev from NETDEV_UP even of another > netdev is going to play way with instance locks and lockdep. > This is likely a false positive but if syzbot keeps complaining > we could: > > diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c > index 995a7207bdf8..f357a7ac70ac 100644 > --- a/drivers/net/wan/lapbether.c > +++ b/drivers/net/wan/lapbether.c > @@ -81,7 +81,7 @@ static struct lapbethdev *lapbeth_get_x25_dev(struct net_device *dev) > > static __inline__ int dev_is_ethdev(struct net_device *dev) > { > - return dev->type == ARPHRD_ETHER && strncmp(dev->name, "dummy", 5); > + return dev->type == ARPHRD_ETHER && !netdev_need_ops_lock(dev); > } > > IDK what the dummy hack is there for, it's been like that since > git begun.. Agreed. The driver itlself looks interesting. IIUC, when loaded, it unconditionally creates virtual netdev for any eth device in the init ns. A bit surprised that syzbot enables it, none of my machines have it enabled.