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Date:   Sat, 30 Jan 2021 09:28:32 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Nikolay Borisov <nborisov@suse.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: kprobes broken since 0d00449c7a28 ("x86: Replace ist_enter()
 with nmi_enter()")
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On Fri, Jan 29, 2021 at 04:24:54PM -0500, Steven Rostedt wrote:
> Specifically, kprobe and ftrace callbacks may have this:
> 
> 	if (in_nmi())
> 		return;
> 
> 	raw_spin_lock_irqsave(&lock, flags);
> 	[..]
> 	raw_spin_unlock_irqrestore(&lock, flags);
> 
> Which is totally fine to have,

Why? There's a distinct lack of explaining here.

Note that we ripped out all such dodgy locking from kretprobes.