Messages in this thread | | | Date | Sun, 22 Jun 2014 22:06:18 +0530 | From | Raghavendra K T <> | Subject | Re: [PATCH 11/11] qspinlock, kvm: Add paravirt support |
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On 06/15/2014 06:17 PM, Peter Zijlstra wrote: > Signed-off-by: Peter Zijlstra<peterz@infradead.org> > --- [...] > + > +void kvm_wait(int *ptr, int val) > +{ > + unsigned long flags; > + > + if (in_nmi()) > + return; > + > + /* > + * Make sure an interrupt handler can't upset things in a > + * partially setup state. > + */
I am seeing hang with even 2 cpu guest (with patches on top of 3.15-rc6 ). looking further with gdb I see one cpu is stuck with native_halt with slowpath flag(_Q_LOCKED_SLOW) set when it was called.
(gdb) bt #0 native_halt () at /test/master/arch/x86/include/asm/irqflags.h:55 #1 0xffffffff81033118 in halt (ptr=0xffffffff81eb0e58, val=524291) at /test/master/arch/x86/include/asm/paravirt.h:116 #2 kvm_wait (ptr=0xffffffff81eb0e58, val=524291) at arch/x86/kernel/kvm.c:835 #3 kvm_wait (ptr=0xffffffff81eb0e58, val=524291) at arch/x86/kernel/kvm.c:809 #4 0xffffffff810a2d8e in pv_wait (lock=0xffffffff81eb0e58) at /test/master/arch/x86/include/asm/paravirt.h:744 #5 __pv_wait_head (lock=0xffffffff81eb0e58) at kernel/locking/qspinlock.c:352
Value of lock seem to be 524288 (means already unlocked?) So apart from races Waiman mentioned, are we also in need of smp_mb() here and/or native_queue_unlock()?.
Interestingly I see other cpu stuck at multi_cpu_stop().
(gdb) thr 1 [Switching to thread 1 (Thread 1)]#0 multi_cpu_stop (data=0xffff8802140d1da0) at kernel/stop_machine.c:192 192 if (msdata->state != curstate) {
Or is it I am missing something.
please let me know if .config need to be shared.
> + local_irq_save(flags); > + > + /* > + * check again make sure it didn't become free while > + * we weren't looking. > + */ > + if (ACCESS_ONCE(*ptr) != val) > + goto out; > + > + /* > + * halt until it's our turn and kicked. Note that we do safe halt > + * for irq enabled case to avoid hang when lock info is overwritten > + * in irq spinlock slowpath and no spurious interrupt occur to save us. > + */ > + if (arch_irqs_disabled_flags(flags)) > + halt(); > + else > + safe_halt(); > + > +out: > + local_irq_restore(flags); > +} > +#endif /* QUEUE_SPINLOCK */
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