From: Oleg Nesterov <oleg@redhat.com>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [Question] smp_wmb() in prepare_uprobe()
Date: Thu, 22 Nov 2018 13:36:56 +0100 [thread overview]
Message-ID: <20181122123655.GD28270@redhat.com> (raw)
In-Reply-To: <20181121224124.GB4016@andrea>
Hi,
On 11/21, Andrea Parri wrote:
>
> The comment for the smp_wmb() in prepare_uprobe() says:
>
> "pairs with rmb() in find_active_uprobe()"
it seems that this comment was wrong from the very beginning,
> but I see no (smp_)rmb() in find_active_uprobe(); I see the smp_rmb() in
> handle_swbp(): is this the intended pairing barrier?
Yes, and the comment near this rmb() says "pairs with wmb() in install_breakpoint()",
today this is not right too.
> Which memory accesses do you want to "order" with this pairing?
See 142b18ddc81439acda4bc4231b291e99fe67d507 ("uprobes: Fix handle_swbp()
vs unregister() + register() race") and the comment above this rmb().
Oleg.
next prev parent reply other threads:[~2018-11-22 12:37 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-21 22:41 [Question] smp_wmb() in prepare_uprobe() Andrea Parri
2018-11-22 12:36 ` Oleg Nesterov [this message]
2018-11-22 13:44 ` Andrea Parri
2018-11-22 15:05 ` Oleg Nesterov
2018-11-22 15:45 ` Andrea Parri
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