Re: [PATCH 09/13] sysfs: Implement sysfs_getattr & sysfs_permission

Serge E. Hallyn
2009-11-04T14:24:25Z

Quoting Eric W. Biederman (ebiederm@xmission.com):
> "Serge E. Hallyn" <serue@us.ibm.com> writes:
>
> > So the inode->i_mutex is not needed?
>
> Good question. Nothing in sysfs needs it. The VFS does not grab the
> inode mutex on this path, but the vfs does grab the inode mutex when
> writing to the inode.

All callers of fs/attr.c:notify_change() do seem to take the i_mutex,
though. And Documentation/filesystem/Locking claims that ->setattr()
does need i_mutex. So I assume that setting of inode->i_ctime etc,
which is what you're doing here, needs to be protected by the i_mutex.

> Since the VFs isn't grabbing the inode_mutex there is probably a race in
> here somewhere if someone looks at things just right.
>
> I am too tired tonight to be that person.

The readers take no lock of any sort (i.e. generic_fillattr and its
callers) so IIUC they could get inconsistent data...

-serge