From: Jiri Olsa <olsajiri@gmail•com>
To: Jakub Kicinski <kuba@kernel•org>,
"Paul E. McKenney" <paulmck@kernel•org>
Cc: Daniel Borkmann <daniel@iogearbox•net>,
Jiri Olsa <olsajiri@gmail•com>, Yonghong Song <yhs@meta•com>,
Alexei Starovoitov <alexei.starovoitov@gmail•com>,
Song Liu <song@kernel•org>, Hao Sun <sunhao.th@gmail•com>,
Peter Zijlstra <peterz@infradead•org>, bpf <bpf@vger•kernel.org>,
Alexei Starovoitov <ast@kernel•org>,
John Fastabend <john.fastabend@gmail•com>,
Andrii Nakryiko <andrii@kernel•org>,
Martin KaFai Lau <martin.lau@linux•dev>,
Yonghong Song <yhs@fb•com>, KP Singh <kpsingh@kernel•org>,
Stanislav Fomichev <sdf@google•com>, Hao Luo <haoluo@google•com>,
David Miller <davem@davemloft•net>,
Jesper Dangaard Brouer <hawk@kernel•org>,
Linux Kernel Mailing List <linux-kernel@vger•kernel.org>,
netdev <netdev@vger•kernel.org>,
Thorsten Leemhuis <regressions@leemhuis•info>
Subject: Re: BUG: unable to handle kernel paging request in bpf_dispatcher_xdp
Date: Sat, 10 Dec 2022 01:06:16 +0100 [thread overview]
Message-ID: <Y5PNeFYJrC6D4P9p@krava> (raw)
In-Reply-To: <20221209153445.22182ca5@kernel.org>
On Fri, Dec 09, 2022 at 03:34:45PM -0800, Jakub Kicinski wrote:
> On Sat, 10 Dec 2022 00:32:07 +0100 Daniel Borkmann wrote:
> > fwiw, these should not be necessary, Documentation/RCU/checklist.rst :
> >
> > [...] One example of non-obvious pairing is the XDP feature in networking,
> > which calls BPF programs from network-driver NAPI (softirq) context. BPF
> > relies heavily on RCU protection for its data structures, but because the
> > BPF program invocation happens entirely within a single local_bh_disable()
> > section in a NAPI poll cycle, this usage is safe. The reason that this usage
> > is safe is that readers can use anything that disables BH when updaters use
> > call_rcu() or synchronize_rcu(). [...]
>
> FWIW I sent a link to the thread to Paul and he confirmed
> the RCU will wait for just the BH.
so IIUC we can omit the rcu_read_lock/unlock on bpf_prog_run_xdp side
Paul,
any thoughts on what we can use in here to synchronize bpf_dispatcher_change_prog
with bpf_prog_run_xdp callers?
with synchronize_rcu_tasks I'm getting splats like:
https://lore.kernel.org/bpf/20221209153445.22182ca5@kernel.org/T/#m0a869f93404a2744884d922bc96d497ffe8f579f
synchronize_rcu_tasks_rude seems to work (patch below), but it also sounds special ;-)
thanks,
jirka
---
diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c
index c19719f48ce0..e6126f07e85b 100644
--- a/kernel/bpf/dispatcher.c
+++ b/kernel/bpf/dispatcher.c
@@ -124,6 +124,7 @@ static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
}
__BPF_DISPATCHER_UPDATE(d, new ?: (void *)&bpf_dispatcher_nop_func);
+ synchronize_rcu_tasks_rude();
if (new)
d->image_off = noff;
next prev parent reply other threads:[~2022-12-10 0:06 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-06 3:28 BUG: unable to handle kernel paging request in bpf_dispatcher_xdp Hao Sun
2022-12-06 6:46 ` Hao Sun
2022-12-06 15:18 ` Jiri Olsa
2022-12-07 19:57 ` Alexei Starovoitov
2022-12-08 17:48 ` Alexei Starovoitov
2022-12-08 18:06 ` Jiri Olsa
2022-12-08 22:26 ` Jiri Olsa
2022-12-08 23:02 ` Jiri Olsa
2022-12-09 7:09 ` Jiri Olsa
2022-12-09 11:22 ` Jiri Olsa
2022-12-09 13:50 ` Jiri Olsa
2022-12-09 15:20 ` Jiri Olsa
2022-12-09 20:31 ` Yonghong Song
2022-12-09 21:53 ` Jiri Olsa
2022-12-09 22:41 ` Daniel Borkmann
2022-12-09 23:07 ` Jiri Olsa
2022-12-09 23:29 ` Jiri Olsa
2022-12-09 23:32 ` Daniel Borkmann
2022-12-09 23:34 ` Jakub Kicinski
2022-12-10 0:06 ` Jiri Olsa [this message]
2022-12-10 0:38 ` Paul E. McKenney
2022-12-10 13:05 ` Jiri Olsa
2022-12-10 1:12 ` Alexei Starovoitov
2022-12-10 13:11 ` Jiri Olsa
2022-12-12 15:04 ` Jiri Olsa
2022-12-13 2:26 ` Hao Sun
2022-12-08 8:44 ` BUG: unable to handle kernel paging request in bpf_dispatcher_xdp #forregzbot Thorsten Leemhuis
2022-12-19 9:59 ` Thorsten Leemhuis
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