linux-kernel - Re: lockups shortly after booting in current git.

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Date:	Thu, 29 Mar 2012 16:26:19 -0400
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: lockups shortly after booting in current git.

On Thu, Mar 29, 2012 at 01:10:21PM -0700, Linus Torvalds wrote:
 > On Thu, Mar 29, 2012 at 12:53 PM, Dave Jones <davej@...hat.com> wrote:
 > >
 > > sysrq-p looks kinda boring. I couldn't get sysrq-l to coincide
 > > with kworker running.
 > 
 > Yeah, none of that looks interesting.
 > 
 > Apparently kworker isn't actually using all CPU after all.

Ok, so progress, kinda.  I can now reproduce it in 10 minutes
just by starting a make -j8 on the kernel, and running fsx in parallel
on the same ssd.

While that's building, I'll click around in firefox, and after a few
minutes, it comes to a standstill. At that point, I can't spawn
new shells. 

kworker does seem to be a red herring. This time, I'm looking at top and..

top - 16:24:02 up 16 min, 10 users,  load average: 11.27, 9.62, 5.58
Tasks: 164 total,   1 running, 163 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.2%us,  3.3%sy,  0.0%ni, 49.1%id, 47.4%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:   3991860k total,  1832652k used,  2159208k free,    67320k buffers
Swap:  6109180k total,        0k used,  6109180k free,   696908k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                 
 1082 root      20   0  175m  20m 9.9m S  4.6  0.5   1:18.24 Xorg                                                                                    
 2918 davej     20   0 15260 1404 1008 R  1.6  0.0   0:17.23 top                                                                                     
    7 root      -2   0     0    0    0 S  0.3  0.0   0:03.38 rcuc/0                         


Pretty dull. Loadavg is consistent at 11, nothing is making forward progress,
and make/fsx are ignoring ctrl-c/ctrl-z

I had a perf top running in another window. It took doesn't show anything exciting..

  8.83%  [kernel]                            [k] read_hpet
  8.26%  [kernel]                            [k] lock_is_held
  5.53%  [kernel]                            [k] __lock_acquire
  4.71%  [kernel]                            [k] sub_preempt_count
  4.32%  [kernel]                            [k] add_preempt_count
  3.90%  [kernel]                            [k] debug_smp_processor_id
  3.86%  [kernel]                            [k] __module_address
  3.24%  [kernel]                            [k] sched_clock_local
  2.92%  [kernel]                            [k] lock_release
  2.91%  [kernel]                            [k] rcu_lockdep_current_cpu_online
  2.22%  [iwlwifi]                           [k] iwl_trans_pcie_read32
  1.92%  [kernel]                            [k] lock_acquired
  1.84%  [kernel]                            [k] match_held_lock
  1.78%  [kernel]                            [k] rcu_is_cpu_idle
  1.76%  [kernel]                            [k] trace_hardirqs_off_caller
  1.72%  [kernel]                            [k] debug_lockdep_rcu_enabled
  1.70%  [kernel]                            [k] native_read_tsc
  1.62%  [kernel]                            [k] local_clock

I'll go back to trying the bisect now that I know how to reproduce it quickly.
Do you think it might be worth restricting the bisect to fs/ ?
Or shall I just do the whole tree bisect from 3.3 ?

	Dave

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