On 10/26, Mikulas Patocka wrote: > > On Fri, 26 Oct 2012, Oleg Nesterov wrote: > > I didn't know about. The code is not reusable, and it doesn't really do > locking.
That was my main point. As for the changing fs/namespace.c to use percpu_rwsem, I am not sure it is that simple and even worthwhile but I won't argue, I do not pretend I understand this code. > > I don't understand why do you both think that __mnt_want_write() > > and mnt_make_readonly() provides the same functionality. I looked > > at this code before I started this patch, and unless I completely > > misread it this does very different things. It is not "lock" at all. > > > > Oleg. > > mnt_want_write uses percpu array of counters, just like percpu semaphores. and this is all imo ;) > The code is different, but it can be changed to use percpu rw semaphores > (if we add percpu_down_write_trylock). I don't really understand how you can make percpu_down_write_trylock() atomic so that it can be called under br_write_lock(vfsmount_lock) in sb_prepare_remount_readonly(). So I guess you also need to replace vfsmount_lock at least. Or _trylock needs the barriers in _down_read. Or I missed something. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
