Messages in this thread Patch in this message | | | Date | Wed, 8 Jul 2015 18:07:50 +0200 | From | Peter Zijlstra <> | Subject | Re: Kernel broken on processors without performance counters |
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On Wed, Jul 08, 2015 at 11:17:38AM -0400, Mikulas Patocka wrote: > Hi > > I found out that the patch a66734297f78707ce39d756b656bfae861d53f62 breaks > the kernel on processors without performance counters, such as AMD K6-3. > Reverting the patch fixes the problem. > > The static key rdpmc_always_available somehow gets set (I couldn't really > find out what is setting it, the function set_attr_rdpmc is not executed), > cr4_set_bits(X86_CR4_PCE) is executed and that results in a crash on boot > when attempting to execute init, because the proecssor doesn't support > that bit in CR4.
Urgh, the static key trainwreck bites again.
One is not supposed to mix static_key_true() and STATIC_KEY_INIT_FALSE.
Does this make it go again?
--- arch/x86/include/asm/mmu_context.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 5e8daee7c5c9..804a3a6030ca 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -23,7 +23,7 @@ extern struct static_key rdpmc_always_available; static inline void load_mm_cr4(struct mm_struct *mm) { - if (static_key_true(&rdpmc_always_available) || + if (static_key_false(&rdpmc_always_available) || atomic_read(&mm->context.perf_rdpmc_allowed)) cr4_set_bits(X86_CR4_PCE); else
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