On Tue, Apr 17, 2012 at 2:14 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
> On Tue, Apr 17, 2012 at 07:28:26PM +0100, Al Viro wrote:>
> Maybe instead I could continue using the i_mutex but handle rename some
> other way; e.g. in delegation code:
>
> if (!mutex_trylock(inode->i_mutex))
> return -EAGAIN;
> if (atomic_read(inode->i_renames_in_progress))
> return -EAGAIN;
>
> and add an
>
> atomic_inc(inode->i_renames_in_progress);
> atomic_dec(inode->i_renames_in_progress);
>
> pair around rename.
Please don't make up your own locking. Plus it's broken anyway, since
a rename could come in directly after your atomic_read (and this is
*why* people shouldn't make up their own locks - they are invariably
broken).
> Or I could increment that counter for all the conflicting operations and
> rely on it instead of the i_mutex. I was trying to avoid adding
> something like that (an inc, a dec, another error path) to every
> operation. And hoping to avoid adding another field to struct inode.
> Oh well.
We could just say that we can do a double inode lock, but then
standardize on the order. And the only sane order is comparing inode
pointers, not inode numbers like ext4 apparently does.
With a standard order, I don't think it would be at all wrong to just
take the inode lock on rename.
Linus
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