linux-kernel - Re: [PATCH] IB/sa: replace GFP_KERNEL with GFP

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Message-ID: <20151027181652.GA6879@obsidianresearch.com>
Date:	Tue, 27 Oct 2015 12:16:52 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	"ira.weiny" <ira.weiny@...el.com>
Cc:	Saurabh Sengar <saurabh.truth@...il.com>, dledford@...hat.com,
	sean.hefty@...el.com, hal.rosenstock@...il.com,
	yun.wang@...fitbricks.com, kaike.wan@...el.com,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/sa: replace GFP_KERNEL with GFP_ATOMIC

On Tue, Oct 27, 2015 at 02:12:36PM -0400, ira.weiny wrote:
> On Tue, Oct 27, 2015 at 09:17:40PM +0530, Saurabh Sengar wrote:
> > replace GFP_KERNEL with GFP_ATOMIC, as code while holding a spinlock
> > should be atomic
> > GFP_KERNEL may sleep and can cause deadlock, where as GFP_ATOMIC may
> > fail but certainly avoids deadlock
> 
> Great catch.  Thanks!
> 
> However, gfp_t is passed to send_mad and we should pass that down and use it.

>         spin_lock_irqsave(&ib_nl_request_lock, flags);
> -       ret = ib_nl_send_msg(query);
> +       ret = ib_nl_send_msg(query, gfp_mask);

A spin lock is guarenteed held around ib_nl_send_msg, so it's
allocations have to be atomic, can't use gfp_mask here..

I do wonder if it is a good idea to call ib_nl_send_msg with a spinlock
held though.. Would be nice to see that go away.

Jason
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