lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Sun, 26 Oct 2014 00:21:31 +0200 (CEST)
From:	Thomas Gleixner <>
To:	Chris Friesen <>
cc:	rt-users <>,
	LKML <>,
	Steven Rostedt <>,
	Peter Zijlstra <>
Subject: Re: semantics of reader/writer semaphores in rt patch

On Sun, 26 Oct 2014, Thomas Gleixner wrote:
> On Thu, 23 Oct 2014, Chris Friesen wrote:
> > Does the RT kernel just disallow this sort of algorithm?
> Yes. For a good reason. Let's add thread C
> A    	   	B		C
> down_read(X)
> 				down_write(X)
> lock(Y)
> modify data
> unlock(Y)
> wake(B)
> 		down_read(X)
> Due to the mainline rwsem fairness semantics:
> A holds X, C is blocked on A and B is blocked on A.
> Deadlock, without RT and the single reader restriction being involved.
> So RT does not violate ANY of the existing mainline semantics, it just
> imposes a performance impact of not allowing multiple readers.

@peterz: It might be worthwhile to have a CONFIG_LOCKDEP=y dependent
mode which restricts concurrent readers to 1 in mainline to catch this
kind of stuff. Hmm?


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists