Messages in this thread | | | Date | Wed, 16 Dec 2009 00:09:24 +0000 | From | Al Viro <> | 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 06:54:37PM -0500, Trond Myklebust wrote:
> > 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.
VM, actually...
> If you want to work around the problem rather than going for something > like Peter's split up of the mmap() callback, then I'd suggest changing > to using nfs_revalidate_mapping_nolock() instead. The fact that we are > seeing these lock misordering warnings is proof that the call to > nfs_revalidate_mapping() is not always a no-op. > > By not taking the i_mutex your call to invalidate_inode_pages2() can > potentially end up racing with another process that is writing to the > file, but that should be a rare occurrence. The effect will be that the > two processes can end up fighting to alternatively dirty and then clean > the pages...
Um... The really interesting question is whether it's a false positive; *can* we hit the deadlock here? getdents() is a red herring; write() and truncate() are real candidates.
What happens if we have one thread do mmap() while another (sharing the address space with it) does write() or truncate() on the same file?
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