This is a note to let you know that I've just added the patch titled
call_function_many: fix list delete vs add race
to the 2.6.38-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
call_function_many-fix-list-delete-vs-add-race.patch
and it can be found in the queue-2.6.38 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From e6cd1e07a185d5f9b0aa75e020df02d3c1c44940 Mon Sep 17 00:00:00 2001
From: Milton Miller <[email protected]>
Date: Tue, 15 Mar 2011 13:27:16 -0600
Subject: call_function_many: fix list delete vs add race
From: Milton Miller <[email protected]>
commit e6cd1e07a185d5f9b0aa75e020df02d3c1c44940 upstream.
Peter pointed out there was nothing preventing the list_del_rcu in
smp_call_function_interrupt from running before the list_add_rcu in
smp_call_function_many.
Fix this by not setting refs until we have gotten the lock for the list.
Take advantage of the wmb in list_add_rcu to save an explicit additional
one.
I tried to force this race with a udelay before the lock & list_add and
by mixing all 64 online cpus with just 3 random cpus in the mask, but
was unsuccessful. Still, inspection shows a valid race, and the fix is
a extension of the existing protection window in the current code.
Reported-by: Peter Zijlstra <[email protected]>
Signed-off-by: Milton Miller <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
kernel/smp.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -491,14 +491,15 @@ void smp_call_function_many(const struct
cpumask_clear_cpu(this_cpu, data->cpumask);
/*
- * To ensure the interrupt handler gets an complete view
- * we order the cpumask and refs writes and order the read
- * of them in the interrupt handler. In addition we may
- * only clear our own cpu bit from the mask.
+ * 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 writen.
+ * The interrupt handler waits until it sees refs filled out
+ * while its cpu mask bit is set; here we may only clear our
+ * own cpu mask bit, and must wait to set refs until we are sure
+ * previous writes are complete and we have obtained the lock to
+ * add the element to the queue.
*/
- smp_wmb();
-
- atomic_set(&data->refs, cpumask_weight(data->cpumask));
raw_spin_lock_irqsave(&call_function.lock, flags);
/*
@@ -507,6 +508,11 @@ void smp_call_function_many(const struct
* 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 order the writes
+ * to func, data, and cpumask before this write to refs.
+ */
+ atomic_set(&data->refs, cpumask_weight(data->cpumask));
raw_spin_unlock_irqrestore(&call_function.lock, flags);
/*
Patches currently in stable-queue which might be from [email protected] are
queue-2.6.38/smp_call_function_many-handle-concurrent-clearing-of-mask.patch
queue-2.6.38/call_function_many-fix-list-delete-vs-add-race.patch
queue-2.6.38/call_function_many-add-missing-ordering.patch
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