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SubjectRe: NFS lockdep lock misordering mmap_sem<->i_mutex_key with 2.6.32-git1
On Mon, Dec 07, 2009 at 02:20:09PM +0100, Andi Kleen wrote:
> > nfs_readdir
> > nfs_do_filldir
> > filldir
> > copy_to_user
> > [page_fault] [grab mmap_sem]
> >
> > sys_mmap [grab mmap_sem]
> > do_mmap_pgoff
> > mmap_region
> > nfs_file_mmap
> > nfs_revalidate_mapping
> > nfs_invalidate_mapping [grab i_mutex]
> >
> > I guess recent lockdep improvement find old bug.
>
> Thanks for the analysis.
>
> I guess should never do copy_*_user while holding i_mutex? There might
> be lots of cases like that.

No. mmap_sem inside i_mutex is the normal order; NFS mmap is doing the
wrong thing here. Note that readdir() vs. NFS (file-only, thankfully ;-)
mmap() is a non-issue; NFS mmap() vs. write() is much more interesting.

Again, a lot of mm/* code expects i_mutex, then mmap_sem order. It's not
just readdir().


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