linux-kernel - Re: [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 27 May 2008 01:47:20 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Miquel van Smoorenburg <mikevs@...all.net>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Glauber Costa <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of
 __GFP_NORETRY

On Tue, 27 May 2008 01:49:47 +0200 Miquel van Smoorenburg <mikevs@...all.net> wrote:

> Please consider the below patch for 2.6.26 (can somebody from the
> x86 team pick this up please? Thank you)
> 
> 
> 
> [PATCH] 2.6.26-rc: x86: pci-dma.c: use __GFP_NO_OOM instead of __GFP_NORETRY
> 
> arch/x86/kernel/pci-dma.c::dma_alloc_coherent() adds __GFP_NORETRY to
> the gfp flags before calling alloc_pages() to prevent the oom killer
> from running.

Now, why does dma_alloc_coherent() do that?

If __GFP_FS is cleared (most cases) then we won't be calling
out_of_memory() anyway.

If __GFP_FS _is_ set then setting __GFP_NORETRY will do much more than
avoiding oom-killings.  It will prevent the page allocator from
retrying and will cause the problems which one assumes (without
evidence :() you have observed.

So...  why not just remove the setting of __GFP_NORETRY?  Why is it
wrong to oom-kill things in this case?

> This has the expected side effect that that alloc_pages() doesn't
> retry anymore. Not really a problem for dma_alloc_coherent(.. GFP_ATOMIC)
> which is the way most drivers use it (through pci_alloc_consistent())
> but drivers that call dma_alloc_coherent(.. GFP_KERNEL) directly can get
> unexpected failures.
> 
> Until we have the mask allocator, use a new flag __GFP_NO_OOM
> instead of __GFP_NORETRY.
> 

But this change increases the chances of a caller getting stuck in the
page allocator for ever, unable to make progress?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/