linux-kernel - Re: [PATCH] kernel/smp: Fix an off by one in csd_lock_wait

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Date:   Thu, 9 Jul 2020 07:36:30 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kaitao Cheng <pilgrimtao@...il.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] kernel/smp: Fix an off by one in csd_lock_wait_toolong()

On Thu, Jul 09, 2020 at 01:49:00PM +0200, Sebastian Andrzej Siewior wrote:
> On 2020-07-09 12:59:06 [+0200], Peter Zijlstra wrote:
> > On Thu, Jul 09, 2020 at 01:48:18PM +0300, Dan Carpenter wrote:
> > > The __per_cpu_offset[] array has "nr_cpu_ids" elements so change the >
> > > >= to prevent a read one element beyond the end of the array.
> > > 
> > > Fixes: 0504bc41a62c ("kernel/smp: Provide CSD lock timeout diagnostics")
> > 
> > I don't have a copy of that patch in my inbox, even though it says Cc:
> > me.
> > 
> > Paul, where do you expect that patch to go? The version I see from my
> > next tree needs a _lot_ of work.
> 
> There is also
>  
>  https://lkml.kernel.org/r/20200705082603.GX3874@shao2-debian
>  https://lkml.kernel.org/r/00000000000042f21905a991ecea@google.com
> 
> it might be the same thing.

Same commit, different bug, but the fix should be in -next by now.
For these two reports, the problem was that I had debug-recording code
on the wrong side of a csd_unlock().

							Thanx, Paul