Re: [RFC 1/2] rwsem: introduce upgrade_read interface

[Matthew Wilcox]

On Wed, Oct 16, 2024 at 10:23:14AM -0400, Waiman Long wrote:
> Another alternative that I have been thinking about is a down_read() variant
> with intention to upgrade later. This will ensure that only one active
> reader is allowed to upgrade later. With this, upgrade_read() will always
> succeed, maybe with some sleeping, as long as the correct down_read() is
> used.

How is that different from Kent's SIX locks other than you can take an
rwsem for write immediately (SIX locks have to be taken for Intent and
then Upgraded)?