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From: Al Viro <viro@ZenIV.linux.org.uk>
To: NeilBrown <neilb@suse.de>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/13] Support follow_link in RCU-walk. - V2
Date: Mon, 16 Mar 2015 19:14:45 +0000	[thread overview]
Message-ID: <20150316191444.GZ29656@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20150316043602.23648.52734.stgit@notabene.brown>

On Mon, Mar 16, 2015 at 03:43:19PM +1100, NeilBrown wrote:
> Hi Al,
>  I believe this series addresses all your concerns about
>  my first attempt.
>  The first patch results in nameidata being almost completely
>  localized to namei.c :-)  It also highlights out-of-date
>  documentation in automount-support.txt :-(
> 
>  It also exposes (and removes) some ... interesting code in lustre.
>  I'm not sure how safe it is to remove that.... I didn't think
>  recursive symlinks used extra stack.

Recursive nested symlinks *do* use extra stack; it's not in fs code, though.
make fs/namei.s and check link_path_walk; AFAICS, on amd64 it's 192 bytes per
level, on sparc64 - 256, sparc32 and ppc32 - 144, ppc64 - obscenely fat 336...

It's more that lustre is an extreme stack hog; call its methods on slightly
deeper stack and you are screwed.  I don't _know_ if that's pure paranoia -
might very well be.  OTOH, it might be not paranoid enough.  OTTH, if it
manages to survive 5 levels on 4K stack, it ought to survive 8 levels on 8K
one; if 3 times the footprint of link_path_walk pushes the total by more 4K,
there's no way in hell to fit 5 times that footprint into 4K stack, nevermind
the rest of call chain...

      parent reply	other threads:[~2015-03-16 19:14 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-16  4:43 NeilBrown
2015-03-16  4:43 ` [PATCH 01/13] VFS: replace {, total_}link_count in task_struct with pointer to nameidata NeilBrown
2015-03-16 19:46   ` Al Viro
2015-03-16  4:43 ` [PATCH 02/13] VFS: make all ->follow_link handlers aware for LOOKUP_RCU NeilBrown
2015-03-16  4:43 ` [PATCH 04/13] security/selinux: check for LOOKUP_RCU in _follow_link NeilBrown
2015-03-16 21:00   ` Al Viro
2015-03-20  4:39     ` NeilBrown
2015-03-20  5:12       ` Al Viro
2015-03-16  4:43 ` [PATCH 03/13] VFS: remove nameidata args from ->follow_link and ->put_link NeilBrown
2015-03-16 20:47   ` Al Viro
2015-03-16  4:43 ` [PATCH 05/13] VFS/namei: use terminate_walk when symlink lookup fails NeilBrown
2015-03-16  4:43 ` [PATCH 12/13] XFS: allow follow_link to often succeed in RCU-walk NeilBrown
2015-03-16 22:37   ` Al Viro
2015-03-16  4:43 ` [PATCH 10/13] VFS/namei: handle LOOKUP_RCU in page_follow_link_light NeilBrown
2015-03-16 22:50   ` Al Viro
2015-03-19 22:38     ` NeilBrown
2015-03-19 23:46       ` Al Viro
2015-03-16  4:43 ` [PATCH 11/13] xfs: use RCU to free 'struct xfs_mount' NeilBrown
2015-03-16  4:43 ` [PATCH 13/13] NFS: support LOOKUP_RCU in nfs_follow_link NeilBrown
2015-03-16  4:43 ` [PATCH 06/13] VFS/namei: new flag to support RCU symlinks: LOOKUP_LINK_RCU NeilBrown
2015-03-16 22:33   ` Al Viro
2015-03-17  0:59     ` Al Viro
2015-03-16  4:43 ` [PATCH 07/13] VFS/namei: abort RCU-walk on symlink if atime needs updating NeilBrown
2015-03-16  4:43 ` [PATCH 08/13] VFS/namei: enhance follow_link to support RCU-walk NeilBrown
2015-03-16  4:43 ` [PATCH 09/13] VFS/namei: enable RCU-walk when following symlinks NeilBrown
2015-03-16 22:44   ` Al Viro
2015-03-16 19:14 ` Al Viro [this message]

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