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From: Steven Rostedt <rostedt@goodmis.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Stefan Metzmacher <metze@samba.org>,
	stable@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] Fix: tracepoint: static call: compare data on transition from 2->1 callees
Date: Thu, 5 Aug 2021 13:07:00 -0400	[thread overview]
Message-ID: <20210805130700.0bc7e52a@oasis.local.home> (raw)
In-Reply-To: <20210805132717.23813-2-mathieu.desnoyers@efficios.com>

On Thu,  5 Aug 2021 09:27:15 -0400
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> On transition from 2->1 callees, we should be comparing .data rather
> than .func, because the same callback can be registered twice with
> different data, and what we care about here is that the data of array
> element 0 is unchanged to skip rcu sync.
> 
> Link: https://lore.kernel.org/io-uring/4ebea8f0-58c9-e571-fd30-0ce4f6f09c70@samba.org/

FYI, You only need to show one Fixes.

> Fixes: d25e37d89dd2 ("tracepoint: Optimize using static_call()")

The above is fixed by the one below. Which means all the stable kernels
that have the above, will also have the below, and thus the above is
just redundant.

> Fixes: 547305a64632 ("tracepoint: Fix out of sync data passing by static caller")

The above is what the patch actually fixes.

> Fixes: 352384d5c84e ("tracepoints: Update static_call before tp_funcs when adding a tracepoint")

How does this patch fix the above? Perhaps the above did not go enough
to fix the issue, but it's unrelated.

I'll remove the first and last Fixes tag.

> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Stefan Metzmacher <metze@samba.org>
> Cc: <stable@vger.kernel.org> # 5.10+

The "# 5.10+" is now obsolete, and not needed. The Fixes tag is used to
determine where this gets backported to.

Other than that. This patch looks good.

-- Steve

> ---
>  kernel/tracepoint.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index fc32821f8240..133b6454b287 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -338,7 +338,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
>  	} else {
>  		rcu_assign_pointer(tp->funcs, tp_funcs);
>  		tracepoint_update_call(tp, tp_funcs,
> -				       tp_funcs[0].func != old[0].func);
> +				       tp_funcs[0].data != old[0].data);
>  	}
>  	release_probes(old);
>  	return 0;


  reply	other threads:[~2021-08-05 17:07 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 13:27 [PATCH 0/3] tracepoint static call fixes Mathieu Desnoyers
2021-08-05 13:27 ` [PATCH 1/3] Fix: tracepoint: static call: compare data on transition from 2->1 callees Mathieu Desnoyers
2021-08-05 17:07   ` Steven Rostedt [this message]
2021-08-05 17:57     ` Mathieu Desnoyers
2021-08-05 13:27 ` [PATCH 2/3] Fix: tracepoint: static call function vs data state mismatch (v2) Mathieu Desnoyers
2021-08-05 18:56   ` Steven Rostedt
2021-08-05 19:15     ` Mathieu Desnoyers
2021-08-05 19:38       ` Steven Rostedt
2021-08-05 19:42         ` Mathieu Desnoyers
2021-08-05 13:27 ` [PATCH 3/3] Fix: tracepoint: rcu get state and cond sync for static call updates (v2) Mathieu Desnoyers
2021-08-05 19:12   ` Steven Rostedt
2021-08-05 19:29     ` [PATCH v3 1/1] Fix: tracepoint: rcu get state and cond sync for static call updates Mathieu Desnoyers

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