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

[Serge E. Hallyn]

Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx):
> "Serge E. Hallyn" <serue@xxxxxxxxxx> 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
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