linux-kernel - Re: [PATCH] uprobes: Fix handle_swbp() vs. unregister() + register() race once more

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Date:   Thu, 22 Nov 2018 17:27:09 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>, stable@...nel.org
Subject: Re: [PATCH] uprobes: Fix handle_swbp() vs. unregister() + register()
 race once more

On 11/22, Oleg Nesterov wrote:
> On 11/22, Andrea Parri wrote:
> >
> > Commit 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() +
> > register() race") added the UPROBE_COPY_INSN flag, and corresponding
> > smp_wmb() and smp_rmb() memory barriers, to ensure that handle_swbp()
> > uses fully-initialized uprobes only.
> > 
> > However, the smp_rmb() is mis-placed: this barrier should be placed
> > after handle_swbp() has tested for the flag, thus guaranteeing that
> > (program-order) subsequent loads from the uprobe can see the initial
> > stores performed by prepare_uprobe().
> > 
> > Move the smp_rmb() accordingly.  Also amend the comments associated
> > to the two memory barriers to indicate their actual locations.
> > 
> > Signed-off-by: Andrea Parri <andrea.parri@...rulasolutions.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Cc: Jiri Olsa <jolsa@...hat.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Oleg Nesterov <oleg@...hat.com>
> > Cc: stable@...nel.org
> > Fixes: 142b18ddc8143 ("uprobes: Fix handle_swbp() vs unregister() + register() race")
> 
> Thanks,
> 
> Acked-by: Oleg Nesterov <oleg@...hat.com>

Yes, but I am not sure this is the -stable material...

Oleg.