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Message-Id: <1278714780-788-1-git-send-email-dvhltc@us.ibm.com>
Date: Fri, 9 Jul 2010 15:32:56 -0700
From: Darren Hart <dvhltc@...ibm.com>
To: linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...e.hu>,
Eric Dumazet <eric.dumazet@...il.com>,
John Kacur <jkacur@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Mike Galbraith <efault@....de>, linux-rt-users@...r.kernel.org
Subject: [PATCH 0/4][RT] futex: fix tasks blocking on two rt_mutex locks
This patch-set address the following problem reported by Mike Galbraith:
> Stress testing, looking to trigger RCU stalls, I've managed to find a
> way to repeatably create fireworks. (got RCU stall, see attached)
>
> 1. download ltp-full-20100630. Needs to be this version because of
> testcase bustage in earlier versions, and must be built with gcc > 4.3,
> else testcases will segfault due to a gcc bug.
>
> 2. apply patchlet so you can run testcases/realtime/perf/latency/run.sh
> at all.
>
> --- pthread_cond_many.c.org 2010-07-05 09:05:59.000000000 +0200
> +++ pthread_cond_many.c 2010-07-04 12:12:25.000000000 +0200
> @@ -259,7 +259,7 @@ void usage(void)
>
> int parse_args(int c, char *v)
> {
> - int handled;
> + int handled = 1;
> switch (c) {
> case 'h':
> usage();
>
> 3. add --realtime for no particular reason.
>
> --- run.sh.org 2010-07-06 15:54:58.000000000 +0200
> +++ run.sh 2010-07-06 16:37:34.000000000 +0200
> @@ -22,7 +22,7 @@ make
> # process to run realtime. The remainder of the processes (if any)
> # will run non-realtime in any case.
>
> -nthread=5000
> +nthread=500
> iter=400
> nproc=5
>
> @@ -39,7 +39,7 @@ i=0
> i=1
> while test $i -lt $nproc
> do
> - ./pthread_cond_many --broadcast -i $iter -n $nthread > $nthread.$iter.$nproc.$i.out &
> + ./pthread_cond_many --realtime --broadcast -i $iter -n $nthread > $nthread.$iter.$nproc.$i.out &
> i=`expr $i + 1`
> done
> wait
The LTP wreckage will be addressed separately <ugh>
> 4. run it.
>
> What happens here is we hit WARN_ON(pendowner->pi_blocked_on != waiter),
> this does not make it to consoles (poking sysrq-foo doesn't either).
> Next comes WARN_ON(!pendowner->pi_blocked_on), followed by the NULL
> explosion, which does make it to consoles.
>
> With explosion avoidance, I also see pendowner->pi_blocked_on->task ==
> NULL at times, but that, as !pendowner->pi_blocked_on, seems to be
> fallout. The start of bad juju is always pi_blocked_on != waiter.
>
> [ 141.609268] BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
> [ 141.609268] IP: [<ffffffff8106856d>] wakeup_next_waiter+0x12c/0x177
> [ 141.609268] PGD 20e174067 PUD 20e253067 PMD 0
> [ 141.609268] Oops: 0000 [#1] PREEMPT SMP
> [ 141.609268] last sysfs file: /sys/devices/system/cpu/cpu3/cache/index2/shared_cpu_map
> [ 141.609268] CPU 0
> [ 141.609268] Pid: 8154, comm: pthread_cond_ma Tainted: G W 2.6.33.6-rt23 #12 MS-7502/MS-7502
> [ 141.609268] RIP: 0010:[<ffffffff8106856d>] [<ffffffff8106856d>] wakeup_next_waiter+0x12c/0x177
> [ 141.609268] RSP: 0018:ffff88020e3cdd78 EFLAGS: 00010097
> [ 141.609268] RAX: 0000000000000000 RBX: ffff8801e8eba5c0 RCX: 0000000000000000
> [ 141.609268] RDX: ffff880028200000 RSI: 0000000000000046 RDI: 0000000000000009
> [ 141.609268] RBP: ffff88020e3cdda8 R08: 0000000000000002 R09: 0000000000000000
> [ 141.609268] R10: 0000000000000005 R11: 0000000000000000 R12: ffffffff81659068
> [ 141.609268] R13: ffff8801e8ebdb58 R14: 0000000000000000 R15: ffff8801e8ebac08
> [ 141.609268] FS: 00007f664d539700(0000) GS:ffff880028200000(0000) knlGS:0000000000000000
> [ 141.609268] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 141.609268] CR2: 0000000000000058 CR3: 0000000214266000 CR4: 00000000000006f0
> [ 141.609268] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 141.609268] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 141.609268] Process pthread_cond_ma (pid: 8154, threadinfo ffff88020e3cc000, task ffff88020e2a4700)
> [ 141.609268] Stack:
> [ 141.609268] 0000000000000000 ffffffff81659068 0000000000000202 0000000000000000
> [ 141.609268] <0> 0000000000000000 0000000080001fda ffff88020e3cddc8 ffffffff812fec48
> [ 141.609268] <0> ffffffff81659068 0000000000606300 ffff88020e3cddd8 ffffffff812ff1b9
> [ 141.609268] Call Trace:
> [ 141.609268] [<ffffffff812fec48>] rt_spin_lock_slowunlock+0x43/0x61
> [ 141.609268] [<ffffffff812ff1b9>] rt_spin_unlock+0x46/0x48
> [ 141.609268] [<ffffffff81067d7f>] do_futex+0x83c/0x935
> [ 141.609268] [<ffffffff810c26ce>] ? handle_mm_fault+0x6de/0x6f1
> [ 141.609268] [<ffffffff81067e36>] ? do_futex+0x8f3/0x935
> [ 141.609268] [<ffffffff81067fba>] sys_futex+0x142/0x154
> [ 141.609268] [<ffffffff81020eb0>] ? do_page_fault+0x23e/0x28e
> [ 141.609268] [<ffffffff81004aa7>] ? math_state_restore+0x3d/0x3f
> [ 141.609268] [<ffffffff81004b08>] ? do_device_not_available+0xe/0x12
> [ 141.609268] [<ffffffff81002c5b>] system_call_fastpath+0x16/0x1b
> [ 141.609268] Code: c7 09 6d 41 81 e8 ac 34 fd ff 4c 39 ab 70 06 00 00 74 11 be 47 02 00 00 48 c7 c7 09 6d 41 81 e8 92 34 fd ff 48 8b 83 70 06 00 00 <4c> 39 60 58 74 11 be 48 02 00 00 48 c7 c7 09 6d 41 81 e8 74 34
> [ 141.609268] RIP [<ffffffff8106856d>] wakeup_next_waiter+0x12c/0x177
> [ 141.609268] RSP <ffff88020e3cdd78>
> [ 141.609268] CR2: 0000000000000058
> [ 141.609268] ---[ end trace 58805b944e6f93ce ]---
> [ 141.609268] note: pthread_cond_ma[8154] exited with preempt_count 2
--
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