Messages in this thread | | | Date | Fri, 27 Sep 2013 13:23:23 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file |
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On Fri, Sep 27, 2013 at 08:02:13AM +0200, Ingo Molnar wrote: > Would be nice to have this as a separate, add-on patch. Every single > instruction removal that has no downside is an upside! > > You can add a comment that explains it.
If someone is going to do add-on patches to the mcslock.h file, please also consider doing a patch that adds comments to the memory barriers in there.
Also, checkpatch.pl should really warn about that; and it appears there code in there for that; however:
# grep -C3 smp_mb scripts/checkpatch.pl } } # check for memory barriers without a comment. if ($line =~ /\b(mb|rmb|wmb|read_barrier_depends|smp_mb|smp_rmb|smp_wmb|smp_read_barrier_depends)\(/) { if (!ctx_has_comment($first_line, $linenr)) { CHK("MEMORY_BARRIER", "memory barrier without comment\n" . $herecurr); # grep -C3 smp_wmb kernel/mutex.c return; } ACCESS_ONCE(prev->next) = node; smp_wmb(); /* Wait until the lock holder passes the lock down */ while (!ACCESS_ONCE(node->locked)) arch_mutex_cpu_relax(); -- arch_mutex_cpu_relax(); } ACCESS_ONCE(next->locked) = 1; smp_wmb(); }
/* # scripts/checkpatch.pl -f kernel/mutex.c 2>&1 | grep memory #
so that appears to be completely broken :/
Joe, any clue what's up with that?
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