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Subject: Re: svn commit: r326218 - head/sys/kern
To: John Baldwin <jhb@freebsd.org>, Nathan Whitehorn <nwhitehorn@freebsd.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org, Konstantin Belousov <kib@FreeBSD.org>,
 "O. Hartmann" <ohartmann@walstatt.org>,
 KrishnamRaju ErapaRaju <Krishna2@chelsio.com>
References: <201711252341.vAPNf5Qx001464@repo.freebsd.org>
 <14322447.103fKFTi3y@ralph.baldwin.cx>
 <3fc45d5f-22b9-0562-278b-c515e36f48e7@freebsd.org>
 <14058479.lc6xlYgyBM@ralph.baldwin.cx>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <2e752d6a-d34a-dde0-acea-fdbf8bebea51@selasky.org>
Date: Wed, 29 Nov 2017 16:33:50 +0100
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Hi Nathan,

The chunk below causes sched_pin() to stop working and should be removed 
from your commit ??!!

It probably explains the hangs seen recently reported by various brave 
people running 12-current :-)

Specifically I see threads migrating between CPUs when td->td_pinned > 0 
using the LinuxKPI RCU API, which in turn leads to a hang when trying to 
synchronize RCU.

--HPS

diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index 5c8bae5afa1..bd4b505f6c3 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -2453,7 +2453,7 @@ sched_add(struct thread *td, int flags)
          * Pick the destination cpu and if it isn't ours transfer to the
          * target cpu.
          */
-       td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to 
start */
+//     td_get_sched(td)->ts_cpu = curcpu; /* Pick something valid to 
start */
         cpu = sched_pickcpu(td, flags);
         tdq = sched_setcpu(td, cpu, flags);
         tdq_add(tdq, td, flags);