linux-kernel - Re: linux-next: manual merge of the akpm tree with the nfs tree

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:	Tue, 31 Jul 2012 16:19:36 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeff Layton <jlayton@...hat.com>
Subject: Re: linux-next: manual merge of the akpm tree with the nfs tree

On Tue, Jul 31, 2012 at 02:37:24PM +0000, Myklebust, Trond wrote:
> On Tue, 2012-07-31 at 11:33 +0100, Mel Gorman wrote:
> > On Tue, Jul 31, 2012 at 02:24:41PM +1000, Stephen Rothwell wrote:
> > > Hi Andrew,
> > > 
> > > Today's linux-next merge of the akpm tree got a conflict in
> > > net/sunrpc/xprtsock.c between commit 5cf02d09b50b ("nfs: skip commit in
> > > releasepage if we're freeing memory for fs-related reasons") from the nfs
> > > tree and commit "nfs: enable swap on NFS" from the akpm tree.
> > > 
> > > Just context changes?  I fixed it up (I think - see below) and can carry
> > > the fix as necessary.
> > 
> > Functionally it looks fine. As you say, it all looks like context
> > changes. Arguably code like this
> > 
> > current->flags &= ~PF_FSTRANS
> > 
> > could use tsk_restore_flags instead() even though it should never be
> > necessary as PF_FSTRANS would not be set on function entry. However,
> > it would set up a depedency between the patch sets that is undesirable.
> > If both sets get merged then it might make sense as a cleanup to use
> > tsk_restore_flags() but not until then.
> > 
> > Thanks Stephen.
> > 
> 
> Do we really need to set both PF_FSTRANS and PF_MEMALLOC here? The
> reason why I merged the PF_FSTRANS patch is that we have the deadlock
> problem when allocating a new socket even before we add swap-over-nfs.
> Adding PF_FSTRANS to disallow entry into the NFS layer by the memory
> allocator fixes that issue.

PF_FSTRANS is to prevent recursion into NFS and is set whether swap-over-NFS
is used or not and for all requests.

> What value does PF_MEMALLOC add? Is that in order to prevent recursion
> into other areas of the swap code (say, if you mix swap-over-nfs with
> ordinary swap-to-disk)?
> 

PF_MEMALLOC is normally to prevent the page reclaim recursing into
itself. Page reclaim can call the page allocator and that cannot re-enter
page reclaim.

In the case of swap-over-NFS, PF_MEMALLOC is set only if the socket is
being used for swapping. In softirq context, the allocation request is
allowed to use PFMEMALLOC reserves to avoid deadlock.

I do not see an obvious way to collapse the two flags together.
PF_FSTRANS should not mean the PFMEMALLOC reserves can be used and
PFMEMALLOC is not set for all requests.

-- 
Mel Gorman
SUSE Labs
--
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/