On Fri, Mar 18, 2011 at 03:28:42PM -0700, [email protected] wrote: > > The patch below does not apply to the .38-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <[email protected]>.
Oops, I applied things out of order, I now got the patch below to apply, sorry for the noise. greg k-h > ------------------ original commit in Linus's tree ------------------ > > >From 723aae25d5cdb09962901d36d526b44d4be1051c Mon Sep 17 00:00:00 2001 > From: Milton Miller <[email protected]> > Date: Tue, 15 Mar 2011 13:27:17 -0600 > Subject: [PATCH] smp_call_function_many: handle concurrent clearing of mask > > Mike Galbraith reported finding a lockup ("perma-spin bug") where the > cpumask passed to smp_call_function_many was cleared by other cpu(s) > while a cpu was preparing its call_data block, resulting in no cpu to > clear the last ref and unlock the block. > > Having cpus clear their bit asynchronously could be useful on a mask of > cpus that might have a translation context, or cpus that need a push to > complete an rcu window. > > Instead of adding a BUG_ON and requiring yet another cpumask copy, just > detect the race and handle it. > > Note: arch_send_call_function_ipi_mask must still handle an empty > cpumask because the data block is globally visible before the that arch > callback is made. And (obviously) there are no guarantees to which cpus > are notified if the mask is changed during the call; only cpus that were > online and had their mask bit set during the whole call are guaranteed > to be called. > > Reported-by: Mike Galbraith <[email protected]> > Reported-by: Jan Beulich <[email protected]> > Acked-by: Jan Beulich <[email protected]> > Cc: [email protected] > Signed-off-by: Milton Miller <[email protected]> > Signed-off-by: Linus Torvalds <[email protected]> > > diff --git a/kernel/smp.c b/kernel/smp.c > index 7c6ded5..9545489 100644 > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -450,7 +450,7 @@ void smp_call_function_many(const struct cpumask *mask, > { > struct call_function_data *data; > unsigned long flags; > - int cpu, next_cpu, this_cpu = smp_processor_id(); > + int refs, cpu, next_cpu, this_cpu = smp_processor_id(); > > /* > * Can deadlock when called with interrupts disabled. > @@ -461,7 +461,7 @@ void smp_call_function_many(const struct cpumask *mask, > WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled() > && !oops_in_progress && !early_boot_irqs_disabled); > > - /* So, what's a CPU they want? Ignoring this one. */ > + /* Try to fastpath. So, what's a CPU they want? Ignoring this one. */ > cpu = cpumask_first_and(mask, cpu_online_mask); > if (cpu == this_cpu) > cpu = cpumask_next_and(cpu, mask, cpu_online_mask); > @@ -519,6 +519,13 @@ void smp_call_function_many(const struct cpumask *mask, > /* We rely on the "and" being processed before the store */ > cpumask_and(data->cpumask, mask, cpu_online_mask); > cpumask_clear_cpu(this_cpu, data->cpumask); > + refs = cpumask_weight(data->cpumask); > + > + /* Some callers race with other cpus changing the passed mask */ > + if (unlikely(!refs)) { > + csd_unlock(&data->csd); > + return; > + } > > raw_spin_lock_irqsave(&call_function.lock, flags); > /* > @@ -532,7 +539,7 @@ void smp_call_function_many(const struct cpumask *mask, > * to the cpumask before this write to refs, which indicates > * data is on the list and is ready to be processed. > */ > - atomic_set(&data->refs, cpumask_weight(data->cpumask)); > + atomic_set(&data->refs, refs); > raw_spin_unlock_irqrestore(&call_function.lock, flags); > > /* > > _______________________________________________ > stable mailing list > [email protected] > http://linux.kernel.org/mailman/listinfo/stable _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
