From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Date: Mon, 29 Jul 2002 20:46:56 +0000 Subject: Re: [Linux-ia64] Linux kernel deadlock caused by spinlock bug Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Mon, Jul 29, 2002 at 03:37:17PM -0500, Van Maren, Kevin wrote: > I changed the code to allow the writer bit to remain set even if > there is a reader. By only allowing a single processor to set > the writer bit, I don't have to worry about pending writers starving > out readers. The potential writer that was able to set the writer bit > gains ownership of the lock when the current readers finish. Since > the retry for read_lock does not keep trying to increment the reader > count, there are no other required changes. however, this is broken. linux relies on being able to do read_lock(x); func() -> func() -> func() -> read_lock(x); if a writer comes between those two read locks, you're toast. i suspect the right answer for the contention you're seeing is an improved get_timeofday which is lockless. -- Revolutions do not require corporate support.