2014-04-02 20:05 GMT+02:00 Paul E. McKenney <paul...@linux.vnet.ibm.com>: > On Wed, Apr 02, 2014 at 06:26:05PM +0200, Frederic Weisbecker wrote: >> diff --git a/kernel/smp.c b/kernel/smp.c >> index 06d574e..bfe7b36 100644 >> --- a/kernel/smp.c >> +++ b/kernel/smp.c >> @@ -265,6 +265,50 @@ int smp_call_function_single_async(int cpu, struct >> call_single_data *csd) >> } >> EXPORT_SYMBOL_GPL(smp_call_function_single_async); >> >> +void generic_smp_queue_function_single_interrupt(void *info) >> +{ >> + struct queue_single_data *qsd = info; >> + >> + WARN_ON_ONCE(xchg(&qsd->pending, 0) != 1); > > I am probably missing something here, but shouldn't this function copy > *qsd to a local on-stack variable before doing the above xchg()? What > prevents the following from happening? > > o CPU 0 does smp_queue_function_single(), which sets ->pending > and fills in ->func and ->data. > > o CPU 1 takes IPI, invoking > generic_smp_queue_function_single_interrupt(). > > o CPU 1 does xchg(), so that ->pending is now zero. > > o An attempt to reuse the queue_single_data sees ->pending equal > to zero, so the ->func and ->data is overwritten. > > o CPU 1 calls the new ->func with the new ->data (or any of the other > two possible unexpected outcomes), which might not be helpful to > the kernel's actuarial statistics. > > So what am I missing?
Ah, I forgot to precise that the function must remain the same for all calls on a single qsd. And the data is always the qsd so this one can only stay stable. So that shouldn't be a problem. But you're right. The fact that we pass the function as an argument of smp_queue_function_single() suggests that we can pass a different function across various calls on a same qsd. So that's confusing. Perhaps changing smp_queue_function_single() such that it only takes the qsd as an argument would make that clearer? Then it's up to the caller to initialize the qsd with the constant function. I could define smp_queue_function_init() for that purpose. Or DEFINE_QUEUE_FUNCTION_DATA() for static initializers. How does that sound? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/