Messages in this thread Patch in this message | | | Date | Wed, 16 Dec 2009 00:38:41 +0100 | From | Andi Kleen <> | Subject | Re: NFS lockdep lock misordering mmap_sem<->i_mutex_key with 2.6.32-git1 |
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On Tue, Dec 15, 2009 at 10:21:34PM +0000, Al Viro wrote: > 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.
I see.
> > Again, a lot of mm/* code expects i_mutex, then mmap_sem order. It's not > just readdir().
I suppose an easy workaround would be to not revalidate in mmap, because open should have already done that?
Very lightly tested RFC patch attached.
-Andi
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NFS: don't revalidate in mmap
nfs_revalidate_mapping takes i_mutex, but mmap already has mmap_sem hold and taking i_mutex inside mmap_sem is not allowed by the VFS.
So don't revalidate on mmap time and trust it has been already done.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
--- fs/nfs/file.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)
Index: linux-2.6.32-ak/fs/nfs/file.c =================================================================== --- linux-2.6.32-ak.orig/fs/nfs/file.c +++ linux-2.6.32-ak/fs/nfs/file.c @@ -297,14 +297,9 @@ nfs_file_mmap(struct file * file, struct dprintk("NFS: mmap(%s/%s)\n", dentry->d_parent->d_name.name, dentry->d_name.name); - /* Note: generic_file_mmap() returns ENOSYS on nommu systems - * so we call that before revalidating the mapping - */ status = generic_file_mmap(file, vma); - if (!status) { + if (!status) vma->vm_ops = &nfs_file_vm_ops; - status = nfs_revalidate_mapping(inode, file->f_mapping); - } return status; } -- ak@linux.intel.com -- Speaking for myself only.
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