From: Matthew Wilcox <willy@debian.org>
To: "Van Maren, Kevin" <kevin.vanmaren@unisys.com>
Cc: "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
"'linux-ia64@linuxia64.org'" <linux-ia64@linuxia64.org>,
"'hpl@cs.utk.edu'" <hpl@cs.utk.edu>
Subject: Re: [Linux-ia64] Linux kernel deadlock caused by spinlock bug
Date: Mon, 29 Jul 2002 21:46:56 +0100 [thread overview]
Message-ID: <20020729214656.B3317@parcelfarce.linux.theplanet.co.uk> (raw)
In-Reply-To: <3FAD1088D4556046AEC48D80B47B478C0101F3AD@usslc-exch-4.slc.unisys.com>; from kevin.vanmaren@unisys.com on Mon, Jul 29, 2002 at 03:37:17PM -0500
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.
next prev parent reply other threads:[~2002-07-29 20:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-07-29 20:37 Linux kernel deadlock caused by spinlock bug Van Maren, Kevin
2002-07-29 20:46 ` Matthew Wilcox [this message]
-- strict thread matches above, loose matches on Subject: below --
2002-07-29 21:05 [Linux-ia64] " Van Maren, Kevin
2002-07-29 21:18 ` Matthew Wilcox
2002-07-30 15:58 ` Russell Lewis
2002-07-30 16:56 ` Richard B. Johnson
2002-07-30 17:02 ` Russell Lewis
2002-07-30 17:14 ` Richard B. Johnson
2002-07-30 22:48 ` Sean Griffin
2002-07-31 17:37 ` Russell Lewis
2002-07-29 21:29 Van Maren, Kevin
2002-07-29 21:48 ` David Mosberger
[not found] <3FAD1088D4556046AEC48D80B47B478C0101F3AE@usslc-exch-4.slc.unisys.com.suse.lists.linux.kernel>
2002-07-30 13:32 ` Andi Kleen
2002-07-30 16:27 ` William Lee Irwin III
2002-07-30 17:06 Van Maren, Kevin
2002-07-30 17:44 ` William Lee Irwin III
2002-07-30 21:15 Van Maren, Kevin
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