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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id s25-20020a056402165900b0051d9dbf5edfsm1714330edx.55.2023.07.28.04.48.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jul 2023 04:48:36 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Fri, 28 Jul 2023 13:48:34 +0200 To: tglozar@redhat.com Cc: linux-kernel@vger.kernel.org, john.fastabend@gmail.com, jakub@cloudflare.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH net] bpf: sockmap: Remove preempt_disable in sock_map_sk_acquire Message-ID: References: <20230728064411.305576-1-tglozar@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230728064411.305576-1-tglozar@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 28, 2023 at 08:44:11AM +0200, tglozar@redhat.com wrote: > From: Tomas Glozar > > Disabling preemption in sock_map_sk_acquire conflicts with GFP_ATOMIC > allocation later in sk_psock_init_link on PREEMPT_RT kernels, since > GFP_ATOMIC might sleep on RT (see bpf: Make BPF and PREEMPT_RT co-exist > patchset notes for details). > > This causes calling bpf_map_update_elem on BPF_MAP_TYPE_SOCKMAP maps to > BUG (sleeping function called from invalid context) on RT kernels. > > preempt_disable was introduced together with lock_sk and rcu_read_lock > in commit 99ba2b5aba24e ("bpf: sockhash, disallow bpf_tcp_close and update > in parallel"), probably to match disabled migration of BPF programs, and > is no longer necessary. > > Remove preempt_disable to fix BUG in sock_map_update_common on RT. FYI, I'm not sure it's related but I started to see following splat recently: [ 189.360689][ T658] ============================= [ 189.361149][ T658] [ BUG: Invalid wait context ] [ 189.361588][ T658] 6.5.0-rc2+ #589 Tainted: G OE [ 189.362174][ T658] ----------------------------- [ 189.362660][ T658] test_progs/658 is trying to lock: [ 189.363176][ T658] ffff8881702652b8 (&psock->link_lock){....}-{3:3}, at: sock_map_update_common+0x1c4/0x340 [ 189.364152][ T658] other info that might help us debug this: [ 189.364689][ T658] context-{5:5} [ 189.365021][ T658] 3 locks held by test_progs/658: [ 189.365508][ T658] #0: ffff888177611a80 (sk_lock-AF_INET){+.+.}-{0:0}, at: sock_map_update_elem_sys+0x82/0x260 [ 189.366503][ T658] #1: ffffffff835a3180 (rcu_read_lock){....}-{1:3}, at: sock_map_update_elem_sys+0x78/0x260 [ 189.367470][ T658] #2: ffff88816cf19240 (&stab->lock){+...}-{2:2}, at: sock_map_update_common+0x12a/0x340 [ 189.368420][ T658] stack backtrace: [ 189.368806][ T658] CPU: 0 PID: 658 Comm: test_progs Tainted: G OE 6.5.0-rc2+ #589 98af30b3c42d747b51da05f1d0e4899e394be6c9 [ 189.369889][ T658] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014 [ 189.370736][ T658] Call Trace: [ 189.371063][ T658] [ 189.371365][ T658] dump_stack_lvl+0xb2/0x120 [ 189.371798][ T658] __lock_acquire+0x9ad/0x2470 [ 189.372243][ T658] ? lock_acquire+0x104/0x350 [ 189.372680][ T658] lock_acquire+0x104/0x350 [ 189.373104][ T658] ? sock_map_update_common+0x1c4/0x340 [ 189.373615][ T658] ? find_held_lock+0x32/0x90 [ 189.374074][ T658] ? sock_map_update_common+0x12a/0x340 [ 189.374587][ T658] _raw_spin_lock_bh+0x38/0x80 [ 189.375060][ T658] ? sock_map_update_common+0x1c4/0x340 [ 189.375571][ T658] sock_map_update_common+0x1c4/0x340 [ 189.376118][ T658] sock_map_update_elem_sys+0x184/0x260 [ 189.376704][ T658] __sys_bpf+0x181f/0x2840 [ 189.377147][ T658] __x64_sys_bpf+0x1a/0x30 [ 189.377556][ T658] do_syscall_64+0x38/0x90 [ 189.377980][ T658] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 [ 189.378473][ T658] RIP: 0033:0x7fe52f47ab5d the patch did not help with that jirka > > Signed-off-by: Tomas Glozar > --- > net/core/sock_map.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index 19538d628714..08ab108206bf 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -115,7 +115,6 @@ static void sock_map_sk_acquire(struct sock *sk) > __acquires(&sk->sk_lock.slock) > { > lock_sock(sk); > - preempt_disable(); > rcu_read_lock(); > } > > @@ -123,7 +122,6 @@ static void sock_map_sk_release(struct sock *sk) > __releases(&sk->sk_lock.slock) > { > rcu_read_unlock(); > - preempt_enable(); > release_sock(sk); > } > > -- > 2.39.3 > >