RE: [PATCH 2/3] rwsem: Implement down_read_interruptible

David Laight
2020-12-08T09:15:03Z

From: Waiman Long
> Sent: 07 December 2020 19:02
...
> > How much more difficult would it be to also add a timeout option?
> > I looked at adding one to the mutex code - and fell into a big pile
> > of replicated code.
> >
> > ISTM that one the initial locked exchange (and spin) fails a few
> > extra instructions when heading for the sleep don't really matter
> >
> Actually, I had tried that before. See
>
> https://lore.kernel.org/lkml/20190911150537.19527-1-longman@redhat.com/
>
> That is for rwsem, but the same can be done for mutex. However, Peter
> didn't seem to like the idea of a timeout parameter. Anyway, it is
> certainly doable if there is a good use case for it.

'Unfortunately' my use-case if for an out-of-tree driver.

The problem I was solving is a status call blocking because
some other code is 'stuck' (probably an oops) with a mutex held.

The code used to use down_timeout() (it was written for 2.4).
When I changed to mutex_(to get optimistic spinning) I lost
the ability to do the timeouts.

David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)