Hi Andrew,
Today's linux-next merge of the akpm tree got a conflict in kernel/smp.c
between commit c7b798525b50 ("smp: Fix SMP function call empty cpu mask race")
from the tip tree and commit "smp: make smp_call_function_many() use logic
similar to smp_call_function_single()" from the akpm tree.
I fixed it up (maybe - see below) and can carry the fix as necessary (no
action is required).
--
Cheers,
Stephen Rothwell s...@canb.auug.org.au
diff --cc kernel/smp.c
index 93e576e,51a81b0..0000000
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@@ -30,10 -21,8 +21,9 @@@ enum
};
struct call_function_data {
- struct call_single_data csd;
- atomic_t refs;
+ struct call_single_data __percpu *csd;
cpumask_var_t cpumask;
+ cpumask_var_t cpumask_ipi;
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
@@@ -482,85 -397,39 +398,45 @@@ void smp_call_function_many(const struc
}
data = &__get_cpu_var(cfd_data);
- csd_lock(&data->csd);
-
- /* This BUG_ON verifies our reuse assertions and can be removed */
- BUG_ON(atomic_read(&data->refs) || !cpumask_empty(data->cpumask));
-
- /*
- * The global call function queue list add and delete are protected
- * by a lock, but the list is traversed without any lock, relying
- * on the rcu list add and delete to allow safe concurrent traversal.
- * We reuse the call function data without waiting for any grace
- * period after some other cpu removes it from the global queue.
- * This means a cpu might find our data block as it is being
- * filled out.
- *
- * We hold off the interrupt handler on the other cpu by
- * ordering our writes to the cpu mask vs our setting of the
- * refs counter. We assert only the cpu owning the data block
- * will set a bit in cpumask, and each bit will only be cleared
- * by the subject cpu. Each cpu must first find its bit is
- * set and then check that refs is set indicating the element is
- * ready to be processed, otherwise it must skip the entry.
- *
- * On the previous iteration refs was set to 0 by another cpu.
- * To avoid the use of transitivity, set the counter to 0 here
- * so the wmb will pair with the rmb in the interrupt handler.
- */
- atomic_set(&data->refs, 0); /* convert 3rd to 1st party write */
- data->csd.func = func;
- data->csd.info = info;
-
- /* Ensure 0 refs is visible before mask. Also orders func and info */
- smp_wmb();
-
- /* 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);
+ if (unlikely(!cpumask_weight(data->cpumask)))
return;
- }
+ /*
+ * After we put an entry into the list, data->cpumask
+ * may be cleared again when another CPU sends another IPI for
+ * a SMP function call, so data->cpumask will be zero.
+ */
+ cpumask_copy(data->cpumask_ipi, data->cpumask);
- raw_spin_lock_irqsave(&call_function.lock, flags);
- /*
- * Place entry at the _HEAD_ of the list, so that any cpu still
- * observing the entry in generic_smp_call_function_interrupt()
- * will not miss any other list entries:
- */
- list_add_rcu(&data->csd.list, &call_function.queue);
- /*
- * We rely on the wmb() in list_add_rcu to complete our writes
- * 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, refs);
- raw_spin_unlock_irqrestore(&call_function.lock, flags);
-
- /*
- * Make the list addition visible before sending the ipi.
- * (IPIs must obey or appear to obey normal Linux cache
- * coherency rules -- see comment in generic_exec_single).
- */
- smp_mb();
+ for_each_cpu(cpu, data->cpumask) {
+ struct call_single_data *csd = per_cpu_ptr(data->csd, cpu);
+ struct call_single_queue *dst =
+ &per_cpu(call_single_queue, cpu);
+ unsigned long flags;
+
+ csd_lock(csd);
+ csd->func = func;
+ csd->info = info;
+
+ raw_spin_lock_irqsave(&dst->lock, flags);
+ list_add_tail(&csd->list, &dst->list);
+ raw_spin_unlock_irqrestore(&dst->lock, flags);
+ }
/* Send a message to all CPUs in the map */
- arch_send_call_function_ipi_mask(data->cpumask);
+ arch_send_call_function_ipi_mask(data->cpumask_ipi);
- /* Optionally wait for the CPUs to complete */
- if (wait)
- csd_lock_wait(&data->csd);
+ if (wait) {
+ for_each_cpu(cpu, data->cpumask) {
+ struct call_single_data *csd =
+ per_cpu_ptr(data->csd, cpu);
+ csd_lock_wait(csd);
+ }
+ }
}
EXPORT_SYMBOL(smp_call_function_many);
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