Re: [PATCH] sysfs_remove_dir Vs dcache_readdir race fix

[Maneesh Soni <maneesh@in.ibm.com>]

On Thu, Nov 20, 2003 at 05:49:57AM +0000, viro@parcelfarce.linux.theplanet.co.uk wrote:
> On Thu, Nov 20, 2003 at 11:17:07AM +0530, Maneesh Soni wrote:
> > Hi,
> > 
> > sysfs_remove_dir modifies d_subdirs list which results in inconsistency
> > when there is concurrent dcache_readdir is going on. I think there
> > is no need for sysfs_remove_dir to modify d_subdirs list and removal
> > of dentries from d_child list is taken care in the final dput().
> 
> WTF?
> 
> All instances of ->readdir() are protected by ->i_sem on parent.  So
> are all operations in sysfs_remove_dir().
> 
> Have you actually observed any race there?

Yes.. if you run the mentioned two loops on an SMP box, you will find that
dcache_readdir is looping with dcache_lock held up in less than a minute. 
The problem comes when sysfs_remove_dir has done list_del_init on the cursor 
dentry which is being used in dcache_readdir. Please enable pr_debug() also 
in sysfs_remove_dir to see the this happening.

Maneesh

-- 
Maneesh Soni
Linux Technology Center, 
IBM Software Lab, Bangalore, India
email: maneesh@in.ibm.com
Phone: 91-80-5044999 Fax: 91-80-5268553
T/L : 9243696