linux-kernel - Re: [PATCH] bpf: don't call mmap_read

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Date: Fri, 14 Jun 2024 09:40:12 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: don't call mmap_read_trylock() from IRQ context

On Fri, Jun 14, 2024 at 8:15 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2024/06/08 20:04, Tetsuo Handa wrote:
> > On 2024/06/08 19:53, Tetsuo Handa wrote:
> >> inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
> >
> > Oops, "inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage." example was
> > found at https://syzkaller.appspot.com/text?tag=CrashReport&x=14f0179a980000 .
> >
> > Then, do we want to
> >
> > -     if (in_hardirq()) {
> > +     if (!in_task()) {
> >
> > instead?
> >
>
> "inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage." upon unlock from IRQ work
> was reported at https://syzkaller.appspot.com/bug?extid=40905bca570ae6784745 .

imo the issue is elsewhere. syzbot reports:
local_lock_acquire include/linux/local_lock_internal.h:29 [inline]
 __mmap_lock_do_trace_released+0x9c/0x620 mm/mmap_lock.c:243
 __mmap_lock_trace_released include/linux/mmap_lock.h:42 [inline]

it complains about:
local_lock(&memcg_paths.lock);
in TRACE_MMAP_LOCK_EVENT.
which looks like a false positive.