Re: frequent lockups in 3.18rc4

[Dave Jones <davej@redhat.com>]

On Mon, Dec 01, 2014 at 12:36:34PM -0800, Linus Torvalds wrote:
 > On Mon, Dec 1, 2014 at 12:28 PM, Dâniel Fraga <fragabr@gmail.com> wrote:
 > >
 > >         Hi Paul. Please, I'd like the patch, because without
 > > preemption, I'm unable to trigger this bug.
 > 
 > Ok, that's already interesting information. And yes, it would probably
 > be interesting to see if CONFIG_PREEMPT=y but !CONFIG_TREE_PREEMPT_RCU
 > then solves it too, to narrow it down to one but not the other..
 > 
 > DaveJ - what about your situation? The standard Fedora kernels use
 > CONFIG_PREEMPT_VOLUNTARY, do you have CONFIG_PREEMPT and
 > CONFIG_TREE_PREEMPT_RCU enabled?

I periodically switch PREEMPT options, just to see if anything new falls
out, though I've been on CONFIG_PREEMPT for quite a while.
So right now I'm testing the TREE_PREEMPT_RCU case.

I'm in the process of bisecting 3.16 -> 3.17 (currently on -rc1)
Thanksgiving kind of screwed up my flow, but 3.16 got a real
pounding for over 3 days with no problems.
I can give a !PREEMPT_RCU build a try, in case that turns out to
point to something quicker than a bisect is going to.

 > I think you and Sasha both saw some RCU oddities too, no?

I don't recall a kernel where I didn't see RCU oddities of some
description, but in recent times, not so much, though a few releases
back I did change some of the RCU related CONFIG options while
Paul & co were chasing down some bugs.

These days I've been running with..

# RCU Subsystem
CONFIG_TREE_PREEMPT_RCU=y
CONFIG_PREEMPT_RCU=y
# CONFIG_TASKS_RCU is not set
CONFIG_RCU_STALL_COMMON=y
# CONFIG_RCU_USER_QS is not set
CONFIG_RCU_FANOUT=64
CONFIG_RCU_FANOUT_LEAF=16
# CONFIG_RCU_FANOUT_EXACT is not set
CONFIG_TREE_RCU_TRACE=y
CONFIG_RCU_BOOST=y
CONFIG_RCU_BOOST_PRIO=1
CONFIG_RCU_BOOST_DELAY=500
CONFIG_RCU_NOCB_CPU=y
# CONFIG_RCU_NOCB_CPU_NONE is not set
# CONFIG_RCU_NOCB_CPU_ZERO is not set
CONFIG_RCU_NOCB_CPU_ALL=y
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
# RCU Debugging
CONFIG_SPARSE_RCU_POINTER=y
# CONFIG_RCU_TORTURE_TEST is not set
CONFIG_RCU_CPU_STALL_TIMEOUT=60
CONFIG_RCU_CPU_STALL_VERBOSE=y
CONFIG_RCU_CPU_STALL_INFO=y
CONFIG_RCU_TRACE=y

	Dave