linux-kernel - Re: Tasks stuck in futex code (in 3.14-rc6)

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Date:	Thu, 20 Mar 2014 11:03:50 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	davidlohr@...com, torvalds@...ux-foundation.org,
	tglx@...utronix.de, mingo@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org, benh@...nel.crashing.org,
	paulus@...ba.org, Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: Tasks stuck in futex code (in 3.14-rc6)

> > Joy,.. let me look at that with ppc in mind.
> 
> OK; so while pretty much all the comments from that patch are utter
> nonsense (what was I thinking), I cannot actually find a real bug.
> 
> But could you try the below which replaces a control dependency with a
> full barrier. The control flow is plenty convoluted that I think the
> control barrier isn't actually valid anymore and that might indeed
> explain the fail.
> 

Unfortunately the patch didnt help. Still seeing tasks stuck

# ps -Ao pid,tt,user,fname,tmout,f,wchan | grep futex
14680 pts/0    root     java         - 0 futex_wait_queue_me
14797 pts/0    root     java         - 0 futex_wait_queue_me
# :> /var/log/messages
# echo t > /proc/sysrq-trigger 
# grep futex_wait_queue_me /var/log/messages | wc -l 
334
#

[ 6904.211478] Call Trace:
[ 6904.211481] [c000000fa1f1b4d0] [0000000000000020] 0x20 (unreliable)
[ 6904.211486] [c000000fa1f1b6a0] [c000000000015208] .__switch_to+0x1e8/0x330
[ 6904.211491] [c000000fa1f1b750] [c000000000702f00] .__schedule+0x360/0x8b0
[ 6904.211495] [c000000fa1f1b9d0] [c000000000147348] .futex_wait_queue_me+0xf8/0x1a0
[ 6904.211500] [c000000fa1f1ba60] [c0000000001486dc] .futex_wait+0x17c/0x2a0
[ 6904.211505] [c000000fa1f1bc10] [c00000000014a614] .do_futex+0x254/0xd80
[ 6904.211510] [c000000fa1f1bd60] [c00000000014b25c] .SyS_futex+0x11c/0x1d0
[ 6904.238874] [c000000fa1f1be30] [c00000000000a0fc] syscall_exit+0x0/0x7c
[ 6904.238879] java            S 00003fff825f6044     0 14682  14076 0x00000080

Is there any other information that I provide that can help?

-- 
Thanks and Regards
Srikar Dronamraju

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