Re: [PATCH v2] PCI: iproc-msi: Removed potentially endless loop handling MSI events

[sashiko-bot@kernel.org]

> The iProc MSI chained handler rereads the event queue tail after each
> batch and keeps processing until the queue is empty. A continuously fed
> queue can therefore keep the CPU in the handler indefinitely, starving
> other interrupts and causing RCU stalls under heavy Ethernet traffic.
> 
> To fix this scenario, remove the loop that keeps reading the head and
> the tail until there are no more pending events. Read the head and tail
> only once and process only the events recorded in that snapshot.
> Update the head before returning. Events arriving during processing
> remain queued for a subsequent parent interrupt, allowing other handlers
> to run without imposing an arbitrary event limit.
> 
> Discovered while testing it with an Ethernet NIC, when too many MSI
> interrupts come in, CPU might get starved:
> 
> [ ... ]
> 
> With this one loop approach, IRQ handler will complete and continue
> to serve MSI events on the next handler invocation.
> 
> Signed-off-by: Eugen Hristev <ehristev@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261103-iproc-irq-v2-1-dc7223df35fc@kernel.org?part=1