2007-09-21 15:39:01

by Chris Friesen

Subject: question on kernel rwsem behaviour

Hi all,

I just had a quick question on read-write semaphore semantics. Suppose
someone holds a sema for reading, then someone else tries to aquire it
for writing, and blocks. Finally, a third code path tries to aquire it
for reading.

Does this third code path get the sema, or does it wait for the writer?

Based on looking at the implementation it seems like it waits, but I'd
like to confirm that.

Thanks,

Chris

2007-09-21 20:13:45

by Peter Zijlstra

Subject: Re: question on kernel rwsem behaviour

On Fri, 21 Sep 2007 09:38:44 -0600 "Chris Friesen"
<[email protected]> wrote:

>
> Hi all,
>
> I just had a quick question on read-write semaphore semantics. Suppose
> someone holds a sema for reading, then someone else tries to aquire it
> for writing, and blocks. Finally, a third code path tries to aquire it
> for reading.
>
> Does this third code path get the sema, or does it wait for the writer?
>
> Based on looking at the implementation it seems like it waits, but I'd
> like to confirm that.

Yes, its fair in that sense.