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From: NeilBrown <neilb@suse.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10/13] VFS/namei: handle LOOKUP_RCU in page_follow_link_light.
Date: Fri, 20 Mar 2015 09:38:33 +1100	[thread overview]
Message-ID: <20150320093833.25603da2@notabene.brown> (raw)
In-Reply-To: <20150316225040.GG29656@ZenIV.linux.org.uk>

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On Mon, 16 Mar 2015 22:50:40 +0000 Al Viro <viro@ZenIV.linux.org.uk> wrote:

> On Mon, Mar 16, 2015 at 03:43:20PM +1100, NeilBrown wrote:
> > +	char *kaddr;
> > +	struct page *page;
> > +	struct address_space *mapping = dentry->d_inode->i_mapping;
> 
> Who said that dentry->d_inode hasn't gone NULL by that point?
> 
> > +	nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);
> 
> ... or changed here.  Again, dentry->d_inode is stable only if you are
> holding a reference to dentry.  That's why we have those dances around
> nd->inode, for example.  Doing unlazy_walk() is enough to stabilize the
> damn thing, so currently ->follow_link() doesn't have to worry about it.
> With your changes, though...

Ahhh - that's what nd->inode is for.  I wondered.

Am I correct in thinking that dentry->d_inode can only become NULL - it cannot
then become some other inode?

In that case the various follow_link methods that are sufficiently atomic for
rcu-walk just need something like:

 struct inode *inode = dentry->d_inode;

 if (!inode)
     return -ECHILD;

If ->d_inode can become another inode, then I suspect we need to pass the
inode as well as the dentry to ->follow_link.


Thanks,
NeilBrown

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  reply	other threads:[~2015-03-19 22:38 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-16  4:43 [PATCH 00/13] Support follow_link in RCU-walk. - V2 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 [this message]
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 ` [PATCH 00/13] Support follow_link in RCU-walk. - V2 Al Viro

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