From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mikulas Patocka <mpatocka@redhat.com>
Subject: Re: [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG
Date: Tue, 24 Apr 2018 11:50:30 -0400 (EDT)
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To: Michal Hocko <mhocko@kernel.org>
Cc: dm-devel@redhat.com, eric.dumazet@gmail.com, mst@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Matthew Wilcox <willy@infradead.org>, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, edumazet@google.com, Andrew Morton <akpm@linux-foundation.org>, David Miller <davem@davemloft.net>, Vlastimil Babka <vbabka@suse.cz>
List-Id: virtualization@lists.linuxfoundation.org



On Tue, 24 Apr 2018, Michal Hocko wrote:

> On Mon 23-04-18 20:06:16, Mikulas Patocka wrote:
> [...]
> > @@ -404,6 +405,12 @@ void *kvmalloc_node(size_t size, gfp_t f
> >  	 */
> >  	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
> >  
> > +#ifdef CONFIG_DEBUG_SG
> > +	/* Catch bugs when the caller uses DMA API on the result of kvmalloc. */
> > +	if (!(prandom_u32_max(2) & 1))
> > +		goto do_vmalloc;
> > +#endif
> 
> I really do not think there is anything DEBUG_SG specific here. Why you
> simply do not follow should_failslab path or even reuse the function?

CONFIG_DEBUG_SG is enabled by default in RHEL and Fedora debug kernel (if 
you don't like CONFIG_DEBUG_SG, pick any other option that is enabled 
there).

Fail-injection framework is if off by default and it must be explicitly 
enabled and configured by the user - and most users won't enable it.

Mikulas

> > +
> >  	/*
> >  	 * We want to attempt a large physically contiguous block first because
> >  	 * it is less likely to fragment multiple larger blocks and therefore
> > @@ -427,6 +434,9 @@ void *kvmalloc_node(size_t size, gfp_t f
> >  	if (ret || size <= PAGE_SIZE)
> >  		return ret;
> >  
> > +#ifdef CONFIG_DEBUG_SG
> > +do_vmalloc:
> > +#endif
> >  	return __vmalloc_node_flags_caller(size, node, flags,
> >  			__builtin_return_address(0));
> >  }
> 
> -- 
> Michal Hocko
> SUSE Labs
>