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List:       linux-kernel
Subject:    Re: [Patch] shm bug introduced with pagecache in 2.3.11
From:       Marcelo Tosatti <marcelo () conectiva ! com ! br>
Date:       1999-11-20 11:40:07
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> > 
> > News servers like Typhoon , high performance threaded web servers (eg Zeus)
> > 
> > Fortunately these guys tend to be using pretty serious I/O subsystems not
> > M/O disks and they are fine with 2.2.
> 
> Well, the more I look at a read-write semaphore, the more I like it: it
> looks like something that once the semaphore implementation itself was
> done, the MM side would be absolutely trivial. It does introduce a new
> issue (multiple threads updating the page tables at the same time), but
> that one doesn't look that horrible..
> 
> We don't ever export the page table handling to the low-level filesystems
> any more (we used to a long time ago: the nopage() function got to touch
> the page tables itself rather than just return the right page), so fixing
> up the new issue is actually a very local fix in mm/mmeory.c.
> 
> Is anybody willing to take a stab at creating a read-write semaphore?
> 
> 		Linus
http://bazar.conectiva.com.br/~marcelo/rwsem-2.3.18ac7.patch
This code is a Linux "port" of the psedo-code implementation found in the
"Unix Kernel Internals" book i wrote some time ago. The patch also
modifies the "uts_sem" semaphore in kernel/sys.c to a rw semaphore.
I've not tested it extensively so there might be ugly bugs/races.
Any construtive comments/bug reports are welcome.


  - Marcelo



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