linux-kernel - Re: [PATCH] mm: fix unexpected changes to {failslab|fail_page

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Date:   Mon, 7 Nov 2022 12:26:21 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     dvyukov@...gle.com, willy@...radead.org, akinobu.mita@...il.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm: fix unexpected changes to
 {failslab|fail_page_alloc}.attr

On Mon, Nov 07, 2022 at 11:05:42PM +0800, Qi Zheng wrote:
> 
> 
> On 2022/11/7 20:42, Jason Gunthorpe wrote:
> > On Mon, Nov 07, 2022 at 11:31:09AM +0800, Qi Zheng wrote:
> > 
> > > @@ -31,9 +33,9 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> > >   		return false;
> > >   	if (gfpflags & __GFP_NOWARN)
> > > -		failslab.attr.no_warn = true;
> > > +		flags |= FAULT_NOWARN;
> > 
> > You should add a comment here about why this is required, to avoid
> > deadlocking printk
> 
> I think this comment should be placed where __GFP_NOWARN is specified
> instead of here. What do you think? :)

NOWARN is clear what it does, it is this specifically that is very
subtle about avoiding deadlock aginst allocations triggered by
printk/etc code.

Jason