Re: [PATCH] Fix the race between the fget() and close()

[Al Viro <viro@ZenIV.linux.org.uk>]

On Tue, Aug 27, 2013 at 01:42:47AM +0100, Al Viro wrote:
> Might be buggered refcounting on struct file somewhere (i.e. extra fput() done,
> getting the file freed *before* close(), leaving a dangling pointer in
> descriptor table).  Might be memory corruption of some kind, slapping junk
> pointer into descriptor table.  Might be buggered refcounting on struct
> dentry - if extra dput() is done somewhere, dentry might get freed under
> us or become negative.
> 
> Hell, might be buggered refcounting on descriptor table - binder is playing
> interesting games there.  Try to reproduce that with CONFIG_DEBUG_KMEMLEAK
> and slab debugging turned on, see if you hit anything from those; if it's
> more or less readily reproducible, I would start with that - too many
> scenarios involve broken refcounting of one sort or another.

Nevermind dentry refcounting - you get NULL dentry, not NULL inode.
Other scenarios still remain, so I'd really recommend slab/kmemleak
debugging turned on.