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authorWill Deacon <will.deacon@arm.com>2018-02-13 13:22:57 +0000
committerIngo Molnar <mingo@kernel.org>2018-02-13 14:50:14 +0100
commit11dc13224c975efcec96647a4768a6f1bb7a19a8 (patch)
tree137d28b601e742a4d05b4720c9a280f867f31609 /kernel/locking
parent95bcade33a8af38755c9b0636e36a36ad3789fe6 (diff)
locking/qspinlock: Ensure node->count is updated before initialising node
When queuing on the qspinlock, the count field for the current CPU's head node is incremented. This needn't be atomic because locking in e.g. IRQ context is balanced and so an IRQ will return with node->count as it found it. However, the compiler could in theory reorder the initialisation of node[idx] before the increment of the head node->count, causing an IRQ to overwrite the initialised node and potentially corrupt the lock state. Avoid the potential for this harmful compiler reordering by placing a barrier() between the increment of the head node->count and the subsequent node initialisation. Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1518528177-19169-3-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/qspinlock.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 348c8cec1042..d880296245c5 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -379,6 +379,14 @@ queue:
tail = encode_tail(smp_processor_id(), idx);
node += idx;
+
+ /*
+ * Ensure that we increment the head node->count before initialising
+ * the actual node. If the compiler is kind enough to reorder these
+ * stores, then an IRQ could overwrite our assignments.
+ */
+ barrier();
+
node->locked = 0;
node->next = NULL;
pv_init_node(node);