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

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Date:   Thu, 22 Nov 2018 20:38:37 +0100
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Oleg Nesterov <oleg@...hat.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 Thu, Nov 22, 2018 at 05:27:09PM +0100, Oleg Nesterov wrote:
> 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>

Thanks, Oleg.


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

I'm inclined to leave it to you/the maintainers in question to decide
about this, ;-)  but please let me know if a resend or another action
is needed from me.

  Andrea


> 
> Oleg.
>