On Sun, Sep 11, 2011 at 12:15:04PM +0100, Al Viro wrote: > write() grabs ->i_mutex on the file it's going to write to. It uses > copy_from_user() while holding ->i_mutex; that can end up calling ->fault(). > If your data comes from the same file mmapped in your address space, you > have xip_write_fault() called while you are in xip_file_write() and *already* > are holding ->i_mutex on the same inode. With your patch it will, AFAICS, > cheerfully deadlock. Oh, wait... You are only doing that to write side of pagefault? That's better, but not much: thread 1: mmap the file, modify mapping thread 2: write() to file The former will do xip_write_fault() while holding ->mmap_sem. The latter will do copy_from_user() from xip_file_write(), getting pagefaults while holding ->i_mutex. Note that we are grabbing ->mmap_sem and ->i_mutex in opposite orders. I.e. that will deadlock on you - all you need is threads sharing the address space. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
