Re: R/W semaphore changes

[Arjan van de Ven <arjan@infradead.org>]

On Tue, 2006-07-04 at 13:47 +0100, David Howells wrote:
> I see you've made some R/W semaphore changes...
> 
> | /*
> |  * nested locking:
> |  */
> 
> This comment is inadequate.  Please be more explicit about when you're allowed
> to do this.
> 
> | extern void down_read_nested(struct rw_semaphore *sem, int subclass);
> | extern void down_write_nested(struct rw_semaphore *sem, int subclass);
> 
> Please, please, please don't.  R/W semaphores are _not_ permitted to nest.

yet they do in places, there where there is a natural hierarchy..

> | # define down_read_nested(sem, subclass)		down_read(sem)
> | # define down_write_nested(sem, subclass)	down_write(sem)
> 
> This is _not_ okay.

why not?



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