Re: 3.1-rc10 oops in nameidata_to_filp

[Andrew Morton <akpm@linux-foundation.org>]

(sorry for the delay)

On Thu, 24 Nov 2011 17:50:03 +0000
Al Viro <viro@ZenIV.linux.org.uk> wrote:

> On Thu, Nov 24, 2011 at 05:38:29PM +0000, Al Viro wrote:
> > Said that, I'm not buying the theory of open assigning to ->f_mapping and
> > screwing it up; all such assignments end up with ->i_mapping of *some*
> > inode, as far as I can see from cursory grep over the tree.  Just in case:
> > do you have CONFIG_FS_POSIX_ACL set?
> 
> BTW, why are we going through that dance with ->host->i_mapping anyway?
> It had been introduced by commit by akpm back in 2004 and from my reading
> of the commit message it was an overkill even back then.  Basically,
> that call got moved to the point past the call of ->open() (good, ->f_mapping
> could've been changed by it) *and* converted from ->f_mapping to
> ->f_mapping->host->i_mapping, which is useless.  Definitely so in the
> case mentioned in that commit (blkdev_open() sets ->f_mapping 
> bdev->bd_inode->i_mapping and that thing will have ->host pointing
> back to bdev->bd_inode).  Commit was in BK, its copy in historical tree
> is commit 1c211088833a27daa4512348bcae9890e8cf92d4
> Author: Andrew Morton <akpm@osdl.org>
> Date:   Wed May 26 17:35:42 2004 -0700
> 
>     [PATCH] Fix the setting of file->f_ra on block-special files
>     
>     We need to set file->f_ra _after_ calling blkdev_open(), when inode->i_mapping
>     points at the right thing.  And we need to get it from
>     inode->i_mapping->host->i_mapping too, which represents the underlying device.
>     
>     Also, don't test for null file->f_mapping in the O_DIRECT checks.
>     
>     Signed-off-by: Andrew Morton <akpm@osdl.org>
> 
> and the only difference wrt setting ->f_mapping on bdev open back then
> is that it used to be done in do_open() instead of blkdev_open() itself.
> So I don't understand what that part of changes had been for...  Andrew?

Beats me, sorry.  Here's the thread:
http://www.gossamer-threads.com/lists/linux/kernel/443511?do=post_view_flat#443511