linux-kernel - Re: [for-next][PATCH 14/15] tracepoint: Do not fail unregistering a probe due to memory failure

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Message-ID: <YBrYx3kCqiEH8HEw@hirez.programming.kicks-ass.net>
Date:   Wed, 3 Feb 2021 18:09:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Florian Weimer <fw@...eb.enyo.de>,
        syzbot+83aa762ef23b6f0d1991@...kaller.appspotmail.com,
        syzbot+d29e58bb557324e55e5e@...kaller.appspotmail.com,
        Matt Mullins <mmullins@...x.us>
Subject: Re: [for-next][PATCH 14/15] tracepoint: Do not fail unregistering a
 probe due to memory failure

On Wed, Feb 03, 2021 at 11:05:31AM -0500, Steven Rostedt wrote:
> +		if (new) {
> +			for (i = 0; old[i].func; i++)
> +				if ((old[i].func != tp_func->func
> +				     || old[i].data != tp_func->data)
> +				    && old[i].func != tp_stub_func)

logical operators go at the end..

> +					new[j++] = old[i];
> +			new[nr_probes - nr_del].func = NULL;
> +			*funcs = new;
> +		} else {
> +			/*
> +			 * Failed to allocate, replace the old function
> +			 * with calls to tp_stub_func.
> +			 */
> +			for (i = 0; old[i].func; i++)

							{

> +				if (old[i].func == tp_func->func &&
> +				    old[i].data == tp_func->data) {

like here.

> +					old[i].func = tp_stub_func;
> +					/* Set the prio to the next event. */
> +					if (old[i + 1].func)
> +						old[i].prio =
> +							old[i + 1].prio;

multi line demands { }, but in this case just don't line-break.

> +					else
> +						old[i].prio = -1;
> +				}

			}

> +			*funcs = old;
> +		}
>  	}
>  	debug_print_probes(*funcs);
>  	return old;
> @@ -295,10 +341,12 @@ static int tracepoint_remove_func(struct tracepoint *tp,
>  	tp_funcs = rcu_dereference_protected(tp->funcs,
>  			lockdep_is_held(&tracepoints_mutex));
>  	old = func_remove(&tp_funcs, func);
> -	if (IS_ERR(old)) {
> -		WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
> +	if (WARN_ON_ONCE(IS_ERR(old)))
>  		return PTR_ERR(old);
> -	}
> +
> +	if (tp_funcs == old)
> +		/* Failed allocating new tp_funcs, replaced func with stub */
> +		return 0;

{ }