Messages in this thread | | | Date | Mon, 21 Jun 2004 17:13:37 -0700 | From | Andrew Morton <> | Subject | Re: deadlocks caused by ext3/reiser dirty_inode calls during do_mmap_pgoff |
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Chris Mason <mason@suse.com> wrote: > > do_mmap_pgoff is called with a write lock on mmap_sem, and can trigger > calls to generic_file_mmap, which calls file_accessed to update the > atime on the file. > > For reiserfs, this might start a transaction, which might have to wait > for the currently running transaction to finish. It looks like ext3 may > do the same thing, but I'm not 100% sure on that. > > If the currently running transaction happens to by running > copy_from_user, like we do during write calls, it might be trying to get > a hold of a read lock on the mmap sem while trying to hand page faults.
heh, good luck writing a testcase.
It's super-improbable because we fault the source page in by hand in generic_file_aio_write_nolock() via fault_in_pages_readable(). Of course, that prefaulting isn't 100% reliable either, because the VM can come in and steal the page (or at least unmap its pte) before we get to doing the copy.
I think we can fix both problems by changing filemap_copy_from_user() and filemap_copy_from_user_iovec() to not fall back to kmap() - just fail the copy in some way if the atomic copy failed. Then, in generic_file_aio_write_nolock(), do a zero-length ->commit_write(), put_page(), then go back and retry the whole thing, starting with fault_in_pages_readable().
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