On Wed, 2018-03-21 at 02:22:28 UTC, Nicholas Piggin wrote:
> 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: 1d607bb3bd ("powerpc/irq: Add mechanism to force a replay of
> interrupts")
> Reported-by: Carol L. Soto <cls...@us.ibm.com>
> Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
Applied to powerpc fixes, thanks.
https://git.kernel.org/powerpc/c/ff6781fd1bb404d8a551c02c35c70c
cheers
