Re: [PATCH] sysfs_remove_dir Vs dcache_readdir race fix

[Dipankar Sarma <dipankar@in.ibm.com>]

On Thu, Nov 20, 2003 at 07:17:09AM -0800, Andrew Morton wrote:
> Maneesh Soni <maneesh@in.ibm.com> wrote:
> >  cpu 0						cpu 1
> >  dcache_dir_open()
> >  --> adds the cursor dentry
> > 
> >  					sysfs_remove_dir()
> >  					--> list_del_init cursor dentry
> > 
> >  dcache_readdir()
> >  --> loops forever on inititalized cursor dentry.
> > 
> > 
> >  Though all these operations happen under parent's i_sem, but it is dropped 
> >  between ->open() and ->readdir() as both are different calls. 
> > 
> >  I think people will also agree that there is no need for sysfs_remove_dir() 
> >  to modify d_subdirs list.
> 
> Seems to me that the libfs code is fragile.
> 
> What happens if the dentry at filp->f_private_data gets moved to a
> different directory after someone did dcache_dir_open()?  Does the loop
> in dcache_readdir() go infinite again?

I am not sure if it is that bad. AFAICS, private_data points to a dummy
dentry marking the current directory read position, that dentry cannot
be moved to a different directory.

Thanks
Dipankar