On Wed, 22 May 2024 11:50:49 +0200 Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> On Wed, May 22, 2024 at 06:59 AM +08, Hillf Danton wrote: > > On Tue, 21 May 2024 08:38:52 -0700 Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> > >> On Sun, May 12, 2024 at 12:22=E2=80=AFAM Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > >> > --- a/net/core/sock_map.c > >> > +++ b/net/core/sock_map.c > >> > @@ -142,6 +142,7 @@ static void sock_map_del_link(struct sock *sk, > >> > bool strp_stop =3D false, verdict_stop =3D false; > >> > struct sk_psock_link *link, *tmp; > >> > > >> > + rcu_read_lock(); > >> > spin_lock_bh(&psock->link_lock); > >> > >> I think this is incorrect. > >> spin_lock_bh may sleep in RT and it won't be safe to do in rcu cs. > > > > Could you specify why it won't be safe in rcu cs if you are right? > > What does rcu look like in RT if not nothing? > > RCU readers can't block, while spinlock RT doesn't disable preemption. > > https://docs.kernel.org/RCU/rcu.html > https://docs.kernel.org/locking/locktypes.html#spinlock-t-and-preempt-rt > > I've finally gotten around to testing proposed fix that just disallows > map_delete_elem on sockmap/sockhash from BPF tracing progs > completely. This should put an end to this saga of syzkaller reports. > > https://lore.kernel.org/all/87jzjnxaqf.fsf@xxxxxxxxxxxxxx/ > The locking info syzbot reported [2] suggests a known issue that like Alexei you hit the send button earlier than expected. 4 locks held by syz-executor361/5090: #0: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline] #0: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline] #0: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: map_delete_elem+0x388/0x5e0 kernel/bpf/syscall.c:1695 #1: ffff88807b2af8f8 (&htab->buckets[i].lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline] #1: ffff88807b2af8f8 (&htab->buckets[i].lock){+...}-{2:2}, at: sock_hash_delete_elem+0x17c/0x400 net/core/sock_map.c:945 #2: ffff88801c2a4290 (&psock->link_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline] #2: ffff88801c2a4290 (&psock->link_lock){+...}-{2:2}, at: sock_map_del_link net/core/sock_map.c:145 [inline] #2: ffff88801c2a4290 (&psock->link_lock){+...}-{2:2}, at: sock_map_unref+0xcc/0x5e0 net/core/sock_map.c:180 #3: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline] #3: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline] #3: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: __bpf_trace_run kernel/trace/bpf_trace.c:2380 [inline] #3: ffffffff8e334d20 (rcu_read_lock){....}-{1:2}, at: bpf_trace_run2+0x114/0x420 kernel/trace/bpf_trace.c:2420 [2] https://lore.kernel.org/all/000000000000d0b87206170dd88f@xxxxxxxxxx/ If CONFIG_PREEMPT_RCU=y rcu_read_lock() does not disable preemption. This is even true for !RT kernels with CONFIG_PREEMPT=y [3] Subject: Re: [patch 30/63] locking/spinlock: Provide RT variant https://lore.kernel.org/all/874kc6rizr.ffs@tglx/
