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SubjectRe: [PATCH] sysfs_remove_dir Vs dcache_readdir race fix
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
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