4.9-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will.deacon@arm.com
[ Upstream commit 11dc13224c975efcec96647a4768a6f1bb7a19a8 ]
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.c... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/locking/qspinlock.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -495,6 +495,14 @@ 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);