Date: Thu, 22 Apr 2004 15:27:05 +0900 From: Kazuaki Oda <kaakun@highway.ne.jp> To: threads@freebsd.org Subject: kse_release and kse_wakeup problem Message-ID: <20040422152705.01f574e1.kaakun@highway.ne.jp>
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Hi,
I think, after switching to use new sleep queue interface, there is a
problem when using scope system threads on MP machine.
This problem occurs when one CPU is executing kse_release and another
is kse_wakeup.
There is a scenario (thread A and B is on the same process):
CPU0: thread A aquires PROC_LOCK in kse_release (kern_thread.c 621)
CPU0: thread A releases PROC_LOCK in msleep (kern_synch.c 209)
CPU1: thread B aquires PROC_LOCK in kse_wakeup (kern_thread.c 667)
CPU1: thread B looks up kse_upcall (kern_thread.c 669-687)
CPU1: thread B gets kse_upcall owner and this is thread A (kern_thread.c 689)
CPU1: thread B sets KUF_DOUPCALL flag (kern_thread.c 697)
because thread A is not on sleep queue yet,
sleepq_abort (kern_thread.c 695) is not executed.
CPU1: thread B releases PROC_LOCK (kern_thread.c 700)
CPU0: thread A puts himself on sleep queue (kern_synch.c 221)
CPU0: thread A sets TDF_SINTR flag (subr_sleepqueue.c 310)
CPU0: thread A sleeps and context switch occurs...
I think, thread B should call sleepq_abort and thread A should do
upcall as soon as possible.
The following patch is for thread A to release PROC_LOCK after putting
himself on sleep queue and setting TDF_SINTR flag.
I don't think this patch is so good (obviously setting TDF_SINTR here is
not good), but enough for test.
And, after patching, MySQL does not hang up on heavy load on my machine
(P4 2.40GHz, HTT enabled).
--- kern_synch.c.orig Thu Apr 22 14:00:40 2004
+++ kern_synch.c Thu Apr 22 12:20:06 2004
@@ -203,11 +203,6 @@
td, p->p_pid, p->p_comm, wmesg, ident);
DROP_GIANT();
- if (mtx != NULL) {
- mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
- WITNESS_SAVE(&mtx->mtx_object, mtx);
- mtx_unlock(mtx);
- }
/*
* We put ourselves on the sleep queue and start our timeout
@@ -219,6 +214,13 @@
* return from cursig().
*/
sleepq_add(sq, ident, mtx, wmesg, 0);
+ if (catch)
+ td->td_flags |= TDF_SINTR;
+ if (mtx != NULL) {
+ mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
+ WITNESS_SAVE(&mtx->mtx_object, mtx);
+ mtx_unlock(mtx);
+ }
if (timo)
sleepq_set_timeout(ident, timo);
if (catch) {
--
Kazuaki Oda <kaakun@highway.ne.jp>
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