Re: [tip: locking/core] lockdep: Fix usage_traceoverflow

[Peter Zijlstra]

On Tue, Oct 27, 2020 at 11:29:35AM +0000, Chris Wilson wrote:
> Quoting tip-bot2 for Peter Zijlstra (2020-10-07 17:20:13)
> > The following commit has been merged into the locking/core branch of tip:
> > 
> > Commit-ID:     24d5a3bffef117ed90685f285c6c9d2faa3a02b4
> > Gitweb:        https://git.kernel.org/tip/24d5a3bffef117ed90685f285c6c9d2faa3a02b4
> > Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > AuthorDate:    Wed, 30 Sep 2020 11:49:37 +02:00
> > Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > CommitterDate: Wed, 07 Oct 2020 18:14:17 +02:00
> > 
> > lockdep: Fix usage_traceoverflow
> > 
> > Basically print_lock_class_header()'s for loop is out of sync with the
> > the size of of ->usage_traces[].
> 
> We're hitting a problem,
> 
> 	$ cat /proc/lockdep_stats
> 
> upon boot generates:
> 
> [   29.465702] DEBUG_LOCKS_WARN_ON(debug_atomic_read(nr_unused_locks) != nr_unused)
> [   29.465716] WARNING: CPU: 0 PID: 488 at kernel/locking/lockdep_proc.c:256 lockdep_stats_show+0xa33/0xac0
> 
> that bisected to this patch. Only just completed the bisection and
> thought you would like a heads up.

Oh hey, that's 'curious'... it does indeed trivially reproduce, let me
have a poke.