linux-kernel - Re: [PATCH 1/2] IB/hfi1: Use preempt_{dis,en}able

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Date:   Fri, 6 Oct 2017 11:19:52 +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>,
        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 1/2] IB/hfi1: Use preempt_{dis,en}able_nort()

On 2017-10-05 18:30:19 [+0200], To Arnaldo Carvalho de Melo wrote:
> On 2017-10-03 12:49:19 [-0300], Arnaldo Carvalho de Melo wrote:
> > From: Arnaldo Carvalho de Melo <acme@...hat.com>
> > 
> > diff --git a/drivers/infiniband/hw/hfi1/pio.c b/drivers/infiniband/hw/hfi1/pio.c
> > index 615be68e40b3..3a30bde9a07b 100644
> > --- a/drivers/infiniband/hw/hfi1/pio.c
> > +++ b/drivers/infiniband/hw/hfi1/pio.c
> > @@ -1421,7 +1421,7 @@ struct pio_buf *sc_buffer_alloc(struct send_context *sc, u32 dw_len,
> >  
> >  	/* there is enough room */
> >  
> > -	preempt_disable();
> > +	preempt_disable_nort();
> >  	this_cpu_inc(*sc->buffers_allocated);
> >  
> >  	/* read this once */
> 
> please replace the preempt_disable() / enable with local_lock() /
> unlock. The section does not look like it could cope with multiple users
> dereferencing / using the same per-CPU variables.

ignore me, there is a spin_lock to protect that…

Sebastian