linux-kernel - Re: [PATCH] tracing/user_events: Run BPF program if attached

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Date:   Tue, 16 May 2023 22:29:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-trace-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
        David Vernet <void@...ifault.com>, dthaler@...rosoft.com,
        brauner@...nel.org, hch@...radead.org
Subject: Re: [PATCH] tracing/user_events: Run BPF program if attached

On Tue, 16 May 2023 18:46:29 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> So don't even ask for other GUP functionality, much less the "remote"
> kind. Not going to happen. If you think you need access to remote
> process memory, you had better do it in process context, or you had
> better just think again.

So this code path is very much in user context (called directly by a
write system call). The issue that Alexei had was that it's also in an
rcu_read_lock() section.

I wonder if this all goes away if we switch to SRCU? That is, sleepable RCU.

-- Steve