linux-kernel - Re: [RFC][PATCH] kmap_atomic

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: Windows password security audit tool. GUI, reports in PDF.

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

Date:	Fri, 09 Oct 2009 00:57:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	jim owens <jowens@...com>
Cc:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Avi Kivity <avi@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC][PATCH] kmap_atomic_push

On Thu, 2009-10-08 at 18:27 -0400, jim owens wrote:
> So if I understand this correctly, the sequence:
> 
> in = kmap_atomic(inpage, KM_USER1);
> 
> out = kmap_atomic(outpage, KM_USER0);
> 
> kunmap_atomic(in, KM_USER1);
> 
> in = kmap_atomic(next_inpage, KM_USER1);
> 
> is now illegal with this patch, which breaks code
> I am testing now for btrfs.
> 
> My code does this because the in/out are zlib inflate
> and the in/out run at different rates.

You can do things like:

do {
 in = kmap_atomic(inpage);
 out = kmap_atomic(outpage);

 <deflate until end of either in/out>

 kunmap_atomic(outpage);
 kunmap_atomic(inpage);

 cond_resched();

 <iterate bits>

} while (<not done>)

The double unmap gives a preemption point, which sounds like a good
thing to have, because your scheme could run for a long while without
enabling preemption, which is badness.

--
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/