Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | Re: [Regression, post-2.6.34-rc1][PATCH] x86 / perf: Fix suspend to RAM on HP nx6325 | Date | Sat, 20 Mar 2010 21:48:01 +0100 |
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On Saturday 20 March 2010, Linus Torvalds wrote: > > On Sat, 20 Mar 2010, Peter Zijlstra wrote: > > > > cpuhw = &per_cpu(cpu_hw_events, cpu); > > + if (!cpuhw) > > + return; > > How can an address-of expression be NULL? > > Yes, 'per_cpu()' is magic, but it shouldn't be possible to be _that_ > magic. It's rather against the whole C model.
Yeah.
A field in the object pointed to by it can be NULL, though.
The appended patch fixes the breakage for me too.
Rafael
--- From: Rafael J. Wysocki <rjw@sisk.pl> Subject: x86 / perf: Fix suspend to RAM on HP nx6325
Commit 3f6da3905398826d85731247e7fbcf53400c18bd (perf: Rework and fix the arch CPU-hotplug hooks) broke suspend to RAM on my HP nx6325 (and most likely on other AMD-based boxes too) by allowing amd_pmu_cpu_offline() to be executed for CPUs that are going offline as part of the suspend process. The problem is that cpuhw->amd_nb may be NULL already when amd_pmu_cpu_offline() is called, so the function should make sure it's not NULL before accessing the object pointed to by it.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> --- arch/x86/kernel/cpu/perf_event_amd.c | 4 ++++ 1 file changed, 4 insertions(+)
Index: linux-2.6/arch/x86/kernel/cpu/perf_event_amd.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/cpu/perf_event_amd.c +++ linux-2.6/arch/x86/kernel/cpu/perf_event_amd.c @@ -348,11 +348,15 @@ static void amd_pmu_cpu_offline(int cpu) raw_spin_lock(&amd_nb_lock); + if (!cpuhw->amd_nb) + goto unlock; + if (--cpuhw->amd_nb->refcnt == 0) kfree(cpuhw->amd_nb); cpuhw->amd_nb = NULL; + unlock: raw_spin_unlock(&amd_nb_lock); }
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