Date: Thu, 4 Feb 2010 00:43:35 +0100 From: Giovanni Trematerra <giovanni.trematerra@gmail.com> To: Brandon Gooch <jamesbrandongooch@gmail.com> Cc: Attilio Rao <attilio@freebsd.org>, FreeBSD Current <freebsd-current@freebsd.org>, Randall Stewart <rrs@lakerest.net> Subject: Re: A strange thing with yesterday's head.. Message-ID: <4e6cba831002031543r391ba4c7m620868fe9cc044a8@mail.gmail.com> In-Reply-To: <179b97fb1002031002g617aee35uec79e3367b2ff7a5@mail.gmail.com> References: <B4F940BE-04BD-4ACC-B686-21D61423D236@lakerest.net> <20100128201520.6a114290@ernst.jennejohn.org> <117532D7-75B9-4BE8-A8B6-0A6761064B92@lakerest.net> <4e6cba831001290744m6067691ct489c61fe9cd28502@mail.gmail.com> <179b97fb1001291212p5b0829f2pea28ab36a85751cf@mail.gmail.com> <4e6cba831002011404h1b6b893cj2390bf0a7560a7f2@mail.gmail.com> <179b97fb1002011424p4a799ff6t8f6b39e6f4b66828@mail.gmail.com> <4e6cba831002022320u2bd5f325m6564556a1abcf4c5@mail.gmail.com> <179b97fb1002031002g617aee35uec79e3367b2ff7a5@mail.gmail.com>
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> Just tried it again (a few times) at r203430, with similar results.
Hi Brandon,
did you update -STABLE? I meant -CURRENT!
Anyway, if you are updating -STABLE, please try the patch below. I
don't know if it applies on -STABLE, let me know.
Thanks for your time.
--
Gianni
--- head/sys/kern/kern_umtx.c 2010/01/10 09:31:57 201991
+++ head/sys/kern/kern_umtx.c 2010/02/03 03:56:32 203414
@@ -2526,6 +2526,12 @@
umtxq_busy(&uq->uq_key);
umtxq_unlock(&uq->uq_key);
+ /*
+ * re-read the state, in case it changed between the try-lock above
+ * and the check below
+ */
+ state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
+
/* set read contention bit */
while ((state & wrflags) && !(state & URWLOCK_READ_WAITERS)) {
oldstate = casuword32(&rwlock->rw_state, state, state |
URWLOCK_READ_WAITERS);
@@ -2658,6 +2664,12 @@
umtxq_busy(&uq->uq_key);
umtxq_unlock(&uq->uq_key);
+ /*
+ * re-read the state, in case it changed between the try-lock above
+ * and the check below
+ */
+ state = fuword32(__DEVOLATILE(int32_t *, &rwlock->rw_state));
+
while (((state & URWLOCK_WRITE_OWNER) || URWLOCK_READER_COUNT(state) != 0) &&
(state & URWLOCK_WRITE_WAITERS) == 0) {
oldstate = casuword32(&rwlock->rw_state, state, state |
URWLOCK_WRITE_WAITERS);
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