linux-kernel - Re: [PATCH 2/2] IB/hfi1: Handle packets in the theaded handler only

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Message-ID: <20171005162730.o4klsmkdcx6xr73g@linutronix.de>
Date:   Thu, 5 Oct 2017 18:27:31 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Clark Williams <williams@...hat.com>,
        Dean Luick <dean.luick@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Julia Cartwright <julia@...com>,
        Kaike Wan <kaike.wan@...el.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        linux-rdma@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Sebastian Sanchez <sebastian.sanchez@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] IB/hfi1: Handle packets in the theaded handler only

On 2017-10-03 12:49:20 [-0300], Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme@...hat.com>
> 
> The hfi1 driver calls request_threaded_irq with two parameters:
> 
>       handler = receive_context_interrupt;
>       thread = receive_context_thread;
>       request_threaded_irq(me->msix.vector, handler, thread, 0, me->name, arg);
> 
> And tries to process packets on the hard irq one, receive_context_interrupt(),
> only waking up the thread (returning IRQ_WAKE_THREAD) when some threshold is
> crossed in the number of packets available in the NIC, trying to balance
> latency and bandwidth.
> 
> But in a CONFIG_PREEMPT_RT_FULL kernel it ends up calling spin locks from the
> hard irq handler (receive_context_interrupt) which causes BUGs like this:

If I am not mistaken current devel-tree of RT (and a few releases before
that) handle that case correctly and force-thread both threads.

Sebastian