This is a note to let you know that I've just added the patch titled

powerpc/64s: Fix lost pending interrupt due to race causing lost update to irq_happened

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: powerpc-64s-fix-lost-pending-interrupt-due-to-race-causing-lost-update-to-irq_happened.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From ff6781fd1bb404d8a551c02c35c70cec1da17ff1 Mon Sep 17 00:00:00 2001

From: Nicholas Piggin npiggin@gmail.com Date: Wed, 21 Mar 2018 12:22:28 +1000 Subject: powerpc/64s: Fix lost pending interrupt due to race causing lost update to irq_happened

From: Nicholas Piggin npiggin@gmail.com

commit ff6781fd1bb404d8a551c02c35c70cec1da17ff1 upstream.

force_external_irq_replay() can be called in the do_IRQ path with interrupts hard enabled and soft disabled if may_hard_irq_enable() set MSR[EE]=1. It updates local_paca->irq_happened with a load, modify, store sequence. If a maskable interrupt hits during this sequence, it will go to the masked handler to be marked pending in irq_happened. This update will be lost when the interrupt returns and the store instruction executes. This can result in unpredictable latencies, timeouts, lockups, etc.

Fix this by ensuring hard interrupts are disabled before modifying irq_happened.

This could cause any maskable asynchronous interrupt to get lost, but it was noticed on P9 SMP system doing RDMA NVMe target over 100GbE, so very high external interrupt rate and high IPI rate. The hang was bisected down to enabling doorbell interrupts for IPIs. These provided an interrupt type that could run at high rates in the do_IRQ path, stressing the race.

Fixes: 1d607bb3bd60 ("powerpc/irq: Add mechanism to force a replay of interrupts") Cc: stable@vger.kernel.org # v4.8+ Reported-by: Carol L. Soto clsoto@us.ibm.com Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/powerpc/kernel/irq.c | 8 ++++++++ 1 file changed, 8 insertions(+)

--- a/arch/powerpc/kernel/irq.c +++ b/arch/powerpc/kernel/irq.c @@ -372,6 +372,14 @@ void force_external_irq_replay(void) */ WARN_ON(!arch_irqs_disabled());

+ /* + * Interrupts must always be hard disabled before irq_happened is + * modified (to prevent lost update in case of interrupt between + * load and store). + */ + __hard_irq_disable(); + local_paca->irq_happened |= PACA_IRQ_HARD_DIS; + /* Indicate in the PACA that we have an interrupt to replay */ local_paca->irq_happened |= PACA_IRQ_EE; }

Patches currently in stable-queue which might be from npiggin@gmail.com are

queue-4.9/powerpc-64s-fix-lost-pending-interrupt-due-to-race-causing-lost-update-to-irq_happened.patch queue-4.9/powerpc-64s-fix-i-side-slb-miss-bad-address-handler-saving-nonvolatile-gprs.patch