From: David Mosberger <davidm@napali.hpl.hp.com>
To: linux-ia64@vger.kernel.org
Subject: Re: [PATCH_TAKE_2] now < last_tick problem
Date: Fri, 10 Oct 2003 16:42:35 +0000 [thread overview]
Message-ID: <marc-linux-ia64-106580483320515@msgid-missing> (raw)
In-Reply-To: <marc-linux-ia64-106575925709435@msgid-missing>
Ian,
Just a quick note (got to run): I think you correctly identified the
race causing the now < last_tick problem. Purely from (bad) memory, I
think the problem was introduced when xtime_lock was converted from an
irq-safe spinlock to a seq-lock. In theory, xtime_lock still protects
get_offset(), but the theory only holds as long as the seq-lock body
is "transactional" (no side-effects until read_seqretry() returns 0).
I think the source of the probem is that we consider the value
returned by get_offset() to be valid EVEN when read_seqretry() returns
1. Because of that, we'll end up updating last_nsec_offset with a
potentialy bad value.
--david
next prev parent reply other threads:[~2003-10-10 16:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-10 4:13 [PATCH_TAKE_2] now < last_tick problem Ian Wienand
2003-10-10 16:42 ` David Mosberger [this message]
2003-10-13 2:11 ` Ian Wienand
2003-10-13 18:17 ` David Mosberger
2003-10-13 23:06 ` Ian Wienand
2003-10-14 5:23 ` David Mosberger
2003-10-14 5:53 ` Ian Wienand
2003-10-14 16:58 ` David Mosberger
2003-10-14 23:05 ` Ian Wienand
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