linux-kernel - Re: [PATCH RFC bpf-next v2 02/10] bpf/helpers: introduce sleepable timers

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Date: Fri, 16 Feb 2024 15:20:06 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Benjamin Tissoires <bentiss@...nel.org>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend
 <john.fastabend@...il.com>, 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>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Jiri Kosina
 <jikos@...nel.org>, Benjamin Tissoires <benjamin.tissoires@...hat.com>,
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-input@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Benjamin Tissoires <bentiss@...nel.org>
Subject: Re: [PATCH RFC bpf-next v2 02/10] bpf/helpers: introduce sleepable
 timers

Just one comment on one of your FIXMEs:

> +	rcu_assign_pointer(t->sleepable_cb_fn, NULL);
> +	/* FIXME: probably do something about the SLEEPABLE flag */

I guess we should store the flag in the timer struct somewhere, and then
restrict the set_callback() functions so that the regular variant only
works without the flag set, and the _sleepable version only works if the
flag is set? Otherwise we may end up calling a non-sleepable function in
sleepable context or vise versa...

-Toke