linux-kernel - Re: Lockdep and rw

lists.openwall.net		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 linux-cve-announce 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:	Tue, 13 Sep 2011 15:07:03 +0100
From:	David Howells <dhowells@...hat.com>
To:	Vladislav Bolkhovitin <vst@...b.net>
Cc:	dhowells@...hat.com, Al Viro <viro@...IV.linux.org.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Lockdep and rw_semaphores

Al is correct.

The in-kernel R/W semaphore implementation is written to be strictly fair.  If
the semaphore is readlocked and a writer is pending, all further readers and
writers get added to the back of the FIFO queue, thus preventing writers from
being starved.

When it comes time to wake someone up, the waiter at the front of the queue is
woken. If that's a reader, then next on the queue may be woken up too if
that's also a reader - up to the point a writer is encountered.  Any readers
beyond that writer in the queue have to wait for the writer in front of them
to get its share first.

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/