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Date: Fri, 25 Apr 2014 09:40:35 +0200
From: Mike Galbraith <umgwanakikbuti@...il.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-rt-users <linux-rt-users@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
John Kacur <jkacur@...hat.com>
Subject: Re: [ANNOUNCE] 3.14-rt1
On Sat, 2014-04-19 at 16:46 +0200, Mike Galbraith wrote:
> Hi Sebastian,
>
> On Fri, 2014-04-11 at 20:57 +0200, Sebastian Andrzej Siewior wrote:
> > Dear RT folks!
> >
> > I'm pleased to announce the v3.14-rt1 patch set.
>
> This hunk in hotplug-light-get-online-cpus.patch looks like a bug.
>
> @@ -333,7 +449,7 @@ static int __ref _cpu_down(unsigned int
> /* CPU didn't die: tell everyone. Can't complain. */
> smpboot_unpark_threads(cpu);
> cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> - goto out_release;
> + goto out_cancel;
> }
> BUG_ON(cpu_online(cpu));
...
BTW, the reason I was eyeballing this stuff is because I was highly
interested in what you were going to do here...
# XXX stomp-machine-deal-clever-with-stopper-lock.patch
...with that bloody lglock. What I did is attached for your amusement.
(warning: viewing may induce "Medussa" syndrome:)
Hotplug can still deadlock in rt trees too, and will if you beat it
hard. The splat below is virgin 3.12-rt (where wonderful lock doesn't
yet exist) while running Stevens stress-cpu-hotplug.sh, which is still
plenty deadly when liberally applied.
[ 161.951908] CPU0 attaching NULL sched-domain.
[ 161.970417] CPU2 attaching NULL sched-domain.
[ 161.976594] CPU3 attaching NULL sched-domain.
[ 161.981044] CPU0 attaching sched-domain:
[ 161.985010] domain 0: span 0,3 level CPU
[ 161.990627] groups: 0 (cpu_power = 997) 3 (cpu_power = 1021)
[ 162.000609] CPU3 attaching sched-domain:
[ 162.007723] domain 0: span 0,3 level CPU
[ 162.012756] groups: 3 (cpu_power = 1021) 0 (cpu_power = 997)
[ 162.025533] smpboot: CPU 2 is now offline
[ 162.036113]
[ 162.036114] ======================================================
[ 162.036115] [ INFO: possible circular locking dependency detected ]
[ 162.036116] 3.12.17-rt25 #14 Not tainted
[ 162.036117] -------------------------------------------------------
[ 162.036118] boot.kdump/6853 is trying to acquire lock:
[ 162.036126] (&hp->lock){+.+...}, at: [<ffffffff81044974>] pin_current_cpu+0x84/0x1d0
[ 162.036126]
[ 162.036126] but task is already holding lock:
[ 162.036131] (&mm->mmap_sem){+++++.}, at: [<ffffffff8156285c>] __do_page_fault+0x14c/0x5d0
[ 162.036132]
[ 162.036132] which lock already depends on the new lock.
[ 162.036132]
[ 162.036133]
[ 162.036133] the existing dependency chain (in reverse order) is:
[ 162.036135]
[ 162.036135] -> #2 (&mm->mmap_sem){+++++.}:
[ 162.036138] [<ffffffff810ae4a8>] check_prevs_add+0xf8/0x180
[ 162.036140] [<ffffffff810aeada>] validate_chain.isra.45+0x5aa/0x750
[ 162.036142] [<ffffffff810af4f6>] __lock_acquire+0x3f6/0x9f0
[ 162.036143] [<ffffffff810b01bc>] lock_acquire+0x8c/0x160
[ 162.036146] [<ffffffff8112df03>] might_fault+0x83/0xb0
[ 162.036149] [<ffffffff81341851>] sel_loadlut+0x11/0x70
[ 162.036152] [<ffffffff8134aa1d>] tioclinux+0x23d/0x2c0
[ 162.036153] [<ffffffff8133f88c>] vt_ioctl+0x86c/0x11f0
[ 162.036155] [<ffffffff81333cf8>] tty_ioctl+0x2a8/0x940
[ 162.036158] [<ffffffff8116c161>] do_vfs_ioctl+0x81/0x340
[ 162.036159] [<ffffffff8116c46b>] SyS_ioctl+0x4b/0x90
[ 162.036162] [<ffffffff81566c22>] system_call_fastpath+0x16/0x1b
[ 162.036164]
[ 162.036164] -> #1 (console_lock){+.+.+.}:
[ 162.036165] [<ffffffff810ae4a8>] check_prevs_add+0xf8/0x180
[ 162.036167] [<ffffffff810aeada>] validate_chain.isra.45+0x5aa/0x750
[ 162.036169] [<ffffffff810af4f6>] __lock_acquire+0x3f6/0x9f0
[ 162.036171] [<ffffffff810b01bc>] lock_acquire+0x8c/0x160
[ 162.036173] [<ffffffff810957bf>] console_lock+0x6f/0x80
[ 162.036174] [<ffffffff8109673d>] console_cpu_notify+0x1d/0x30
[ 162.036176] [<ffffffff81562d3d>] notifier_call_chain+0x4d/0x70
[ 162.036179] [<ffffffff81070b49>] __raw_notifier_call_chain+0x9/0x10
[ 162.036181] [<ffffffff8104443b>] __cpu_notify+0x1b/0x30
[ 162.036182] [<ffffffff81044650>] cpu_notify_nofail+0x10/0x20
[ 162.036185] [<ffffffff815480fd>] _cpu_down+0x20d/0x440
[ 162.036186] [<ffffffff81548360>] cpu_down+0x30/0x50
[ 162.036188] [<ffffffff8137118c>] cpu_subsys_offline+0x1c/0x30
[ 162.036191] [<ffffffff8136c285>] device_offline+0x95/0xc0
[ 162.036192] [<ffffffff8136c390>] online_store+0x40/0x80
[ 162.036194] [<ffffffff813697c3>] dev_attr_store+0x13/0x30
[ 162.036197] [<ffffffff811c8820>] sysfs_write_file+0xf0/0x170
[ 162.036200] [<ffffffff8115a068>] vfs_write+0xc8/0x1d0
[ 162.036202] [<ffffffff8115a500>] SyS_write+0x50/0xa0
[ 162.036203] [<ffffffff81566c22>] system_call_fastpath+0x16/0x1b
[ 162.036205]
[ 162.036205] -> #0 (&hp->lock){+.+...}:
[ 162.036207] [<ffffffff810ae39d>] check_prev_add+0x7bd/0x7d0
[ 162.036209] [<ffffffff810ae4a8>] check_prevs_add+0xf8/0x180
[ 162.036210] [<ffffffff810aeada>] validate_chain.isra.45+0x5aa/0x750
[ 162.036212] [<ffffffff810af4f6>] __lock_acquire+0x3f6/0x9f0
[ 162.036214] [<ffffffff810b01bc>] lock_acquire+0x8c/0x160
[ 162.036216] [<ffffffff8155e645>] rt_spin_lock+0x55/0x70
[ 162.036218] [<ffffffff81044974>] pin_current_cpu+0x84/0x1d0
[ 162.036220] [<ffffffff81079ef1>] migrate_disable+0x81/0x100
[ 162.036222] [<ffffffff8112fd38>] handle_pte_fault+0xf8/0x1c0
[ 162.036223] [<ffffffff81131646>] __handle_mm_fault+0x106/0x1b0
[ 162.036225] [<ffffffff81131712>] handle_mm_fault+0x22/0x30
[ 162.036227] [<ffffffff815628c1>] __do_page_fault+0x1b1/0x5d0
[ 162.036229] [<ffffffff81562ce9>] do_page_fault+0x9/0x10
[ 162.036230] [<ffffffff8155f9d2>] page_fault+0x22/0x30
[ 162.036232] [<ffffffff81566b0f>] ret_from_fork+0xf/0xb0
[ 162.036233]
[ 162.036233] other info that might help us debug this:
[ 162.036233]
[ 162.036235] Chain exists of:
[ 162.036235] &hp->lock --> console_lock --> &mm->mmap_sem
[ 162.036235]
[ 162.036236] Possible unsafe locking scenario:
[ 162.036236]
[ 162.036236] CPU0 CPU1
[ 162.036237] ---- ----
[ 162.036238] lock(&mm->mmap_sem);
[ 162.036239] lock(console_lock);
[ 162.036241] lock(&mm->mmap_sem);
[ 162.036242] lock(&hp->lock);
[ 162.036242]
[ 162.036242] *** DEADLOCK ***
[ 162.036242]
[ 162.036243] 1 lock held by boot.kdump/6853:
[ 162.036247] #0: (&mm->mmap_sem){+++++.}, at: [<ffffffff8156285c>] __do_page_fault+0x14c/0x5d0
[ 162.036247]
[ 162.036247] stack backtrace:
[ 162.036250] CPU: 0 PID: 6853 Comm: boot.kdump Not tainted 3.12.17-rt25 #14
[ 162.036251] Hardware name: MEDIONPC MS-7502/MS-7502, BIOS 6.00 PG 12/26/2007
[ 162.036253] ffff8801fd0e6d58 ffff8800bbe85918 ffffffff8155532c 0000000000000000
[ 162.036255] 0000000000000000 ffff8800bbe85968 ffffffff8154d07f ffff8800bbe85958
[ 162.036257] ffffffff82350640 ffff8801fd0e6d58 ffff8801fd0e6d20 ffff8801fd0e6d58
[ 162.036258] Call Trace:
[ 162.036261] [<ffffffff8155532c>] dump_stack+0x4f/0x91
[ 162.036263] [<ffffffff8154d07f>] print_circular_bug+0xd3/0xe4
[ 162.036265] [<ffffffff810ae39d>] check_prev_add+0x7bd/0x7d0
[ 162.036268] [<ffffffff8107e1f5>] ? sched_clock_local+0x25/0x90
[ 162.036270] [<ffffffff8107e388>] ? sched_clock_cpu+0xa8/0x120
[ 162.036272] [<ffffffff810ae4a8>] check_prevs_add+0xf8/0x180
[ 162.036273] [<ffffffff810aeada>] validate_chain.isra.45+0x5aa/0x750
[ 162.036275] [<ffffffff810af4f6>] __lock_acquire+0x3f6/0x9f0
[ 162.036277] [<ffffffff8155d9b1>] ? rt_spin_lock_slowlock+0x231/0x280
[ 162.036279] [<ffffffff8155d8b1>] ? rt_spin_lock_slowlock+0x131/0x280
[ 162.036281] [<ffffffff81044974>] ? pin_current_cpu+0x84/0x1d0
[ 162.036282] [<ffffffff810b01bc>] lock_acquire+0x8c/0x160
[ 162.036284] [<ffffffff81044974>] ? pin_current_cpu+0x84/0x1d0
[ 162.036286] [<ffffffff8155e645>] rt_spin_lock+0x55/0x70
[ 162.036288] [<ffffffff81044974>] ? pin_current_cpu+0x84/0x1d0
[ 162.036289] [<ffffffff81044974>] pin_current_cpu+0x84/0x1d0
[ 162.036291] [<ffffffff81079ef1>] migrate_disable+0x81/0x100
[ 162.036293] [<ffffffff8112fd38>] handle_pte_fault+0xf8/0x1c0
[ 162.036295] [<ffffffff8156285c>] ? __do_page_fault+0x14c/0x5d0
[ 162.036296] [<ffffffff81131646>] __handle_mm_fault+0x106/0x1b0
[ 162.036298] [<ffffffff81131712>] handle_mm_fault+0x22/0x30
[ 162.036300] [<ffffffff815628c1>] __do_page_fault+0x1b1/0x5d0
[ 162.036302] [<ffffffff8107e1f5>] ? sched_clock_local+0x25/0x90
[ 162.036304] [<ffffffff810790d1>] ? get_parent_ip+0x11/0x50
[ 162.036306] [<ffffffff81562f7d>] ? add_preempt_count.part.93+0x5d/0xb0
[ 162.036307] [<ffffffff810aa2c2>] ? get_lock_stats+0x22/0x70
[ 162.036309] [<ffffffff810aa7ce>] ? put_lock_stats.isra.26+0xe/0x40
[ 162.036311] [<ffffffff812841ed>] ? trace_hardirqs_off_thunk+0x3a/0x3c
[ 162.036313] [<ffffffff81562ce9>] do_page_fault+0x9/0x10
[ 162.036315] [<ffffffff8155f9d2>] page_fault+0x22/0x30
[ 162.036317] [<ffffffff81284130>] ? __put_user_4+0x20/0x30
[ 162.036319] [<ffffffff81078c47>] ? schedule_tail+0x67/0xb0
[ 162.036321] [<ffffffff81566b0f>] ret_from_fork+0xf/0xb0
View attachment "stomp-machine-create-lg_global_trylock_relax.patch" of type "text/x-patch" (2102 bytes)
View attachment "stomp-machine-deal-clever-with-stopper-lock.patch" of type "text/x-patch" (2717 bytes)
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