On Tue, 2012-05-15 at 19:31 +0200, Peter Zijlstra wrote:

On Tue, 2012-05-15 at 13:25 -0400, Steven Rostedt wrote:

quoted

On Tue, 2012-05-15 at 11:42 -0400, Steven Rostedt wrote:

quoted

On Tue, 2012-05-15 at 17:06 +0200, Peter Zijlstra wrote:

quoted

On Tue, 2012-05-15 at 10:03 -0400, Steven Rostedt wrote:

quoted

where readers may nest (the same task may grab the same rwsem for
read multiple times), but only one task may hold the rwsem at any
given
time (for read or write).

Humm, that sounds iffy, rwsem isn't a recursive read lock only rwlock_t
is.

In that case, current -rt is broken. As it has it being a recursive lock
(without my patch).

Nah not broken, just pointless. A recursive lock that's not used
recursively is fine.

Heh, sure :-) But as -rt keeps it recursive, I didn't want to change
that.

quoted

Why wouldn't it be recursive. If two different tasks are allowed to grab
a read lock at the same time, why can't the same task grab a read lock
twice? As long as it releases it the same amount of times.

Now you can't grab a read lock if you have the write lock.

rwsem is fifo-fair, if a writer comes in between the second read
acquisition (even by the same task) would block and you'd be a deadlock
since the write won't succeed since you're still holding a reader.

Yep agreed. And this patch didn't change that either.

-- Steve