Date:	Fri, 13 Feb 2015 14:21:25 -0700
From:	Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thavatchai Makphaibulchoke <tmac@...com>
CC:	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, tglx@...utronix.de,
	linux-rt-users@...r.kernel.org
Subject: Re: [PATCH RT v2] kernel/res_counter.c: Change lock of struct res_counter
 to raw_spinlock_t



On 02/13/2015 12:19 PM, Paul Gortmaker wrote:
> 
> I think there is more to this issue than just a lock conversion.
> Firstly, if we look at the existing -rt patches, we've got the old
> patch from ~2009 that is:
> 

Thanks Paul for testing and reporting the problem.

Yes, looks like the issue probably involve more than converting to a
raw_spinlock_t.

>  From: Ingo Molnar <mingo@...e.hu>
>  Date: Fri, 3 Jul 2009 08:44:33 -0500
>  Subject: [PATCH] core: Do not disable interrupts on RT in res_counter.c
> 
> which changed the local_irq_save to local_irq_save_nort in order to
> avoid such a raw lock conversion.
> 

The patch did not quite state explicitly that the fix was to avoid raw
lock conversion.  I guess one could infer so.

Anyway as the patch also mentioned, the code needs a second look.

I'll try to see if I could rework my patch.

> Also, when I test this patch on a larger machine with lots of cores, I
> get boot up issues (general protection fault while trying to access the
> raw lock) or RCU stalls that trigger broadcast NMI backtraces; both which
> implicate the same code area, and they go away with a revert.
> 

Could you please let me know how many cores/threads you are running.

Could you please also send me a stack trace for the protection fault
problem, if available.

Thanks again for reporting the problem.

Thanks,
Mak.


> Stuff like the below. Figured I'd better mention it since Steve was
> talking about rounding up patches for stable, and the solution to the
> original problem reported here seems to need to be revisited.
> 
> Paul.
> --
> 
> 
> [   38.615736] NMI backtrace for cpu 15
> [   38.615739] CPU: 15 PID: 835 Comm: ovirt-engine.py Not tainted 3.14.33-rt28-WR7.0.0.0_ovp+ #3
> [   38.615740] Hardware name: Intel Corporation S2600CP/S2600CP, BIOS SE5C600.86B.02.01.0002.082220131453 08/22/2013
> [   38.615742] task: ffff880faca80000 ti: ffff880f9d890000 task.ti: ffff880f9d890000
> [   38.615751] RIP: 0010:[<ffffffff810820a1>]  [<ffffffff810820a1>] preempt_count_add+0x41/0xb0
> [   38.615752] RSP: 0018:ffff880ffd5e3d00  EFLAGS: 00000097
> [   38.615754] RAX: 0000000000010002 RBX: 0000000000000001 RCX: 0000000000000000
> [   38.615755] RDX: 0000000000000000 RSI: 0000000000000100 RDI: 0000000000000001
> [   38.615756] RBP: ffff880ffd5e3d08 R08: ffffffff82317700 R09: 0000000000000028
> [   38.615757] R10: 000000000000000f R11: 0000000000017484 R12: 0000000000044472
> [   38.615758] R13: 000000000000000f R14: 00000000c42caa68 R15: 0000000000000010
> [   38.615760] FS:  00007effa30c2700(0000) GS:ffff880ffd5e0000(0000) knlGS:0000000000000000
> [   38.615761] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   38.615762] CR2: 00007f19e3c29320 CR3: 0000000f9f9a3000 CR4: 00000000001407e0
> [   38.615763] Stack:
> [   38.615765]  00000000c42caa20 ffff880ffd5e3d38 ffffffff8140e524 0000000000001000
> [   38.615767]  00000000000003e9 0000000000000400 0000000000000002 ffff880ffd5e3d48
> [   38.615769]  ffffffff8140e43f ffff880ffd5e3d58 ffffffff8140e477 ffff880ffd5e3d78
> [   38.615769] Call Trace:
> [   38.615771]  <IRQ>
> [   38.615779]  [<ffffffff8140e524>] delay_tsc+0x44/0xd0
> [   38.615782]  [<ffffffff8140e43f>] __delay+0xf/0x20
> [   38.615784]  [<ffffffff8140e477>] __const_udelay+0x27/0x30
> [   38.615788]  [<ffffffff810355da>] native_safe_apic_wait_icr_idle+0x2a/0x60
> [   38.615792]  [<ffffffff81036c80>] default_send_IPI_mask_sequence_phys+0xc0/0xe0
> [   38.615798]  [<ffffffff8103a5f7>] physflat_send_IPI_all+0x17/0x20
> [   38.615801]  [<ffffffff81036e80>] arch_trigger_all_cpu_backtrace+0x70/0xb0
> [   38.615807]  [<ffffffff810b4d41>] rcu_check_callbacks+0x4f1/0x840
> [   38.615814]  [<ffffffff8105365e>] ? raise_softirq_irqoff+0xe/0x40
> [   38.615821]  [<ffffffff8105cc52>] update_process_times+0x42/0x70
> [   38.615826]  [<ffffffff810c0336>] tick_sched_handle.isra.15+0x36/0x50
> [   38.615829]  [<ffffffff810c0394>] tick_sched_timer+0x44/0x70
> [   38.615835]  [<ffffffff8107598b>] __run_hrtimer+0x9b/0x2a0
> [   38.615838]  [<ffffffff810c0350>] ? tick_sched_handle.isra.15+0x50/0x50
> [   38.615842]  [<ffffffff81076cbe>] hrtimer_interrupt+0x12e/0x2e0
> [   38.615845]  [<ffffffff810352c7>] local_apic_timer_interrupt+0x37/0x60
> [   38.615851]  [<ffffffff81a376ef>] smp_apic_timer_interrupt+0x3f/0x50
> [   38.615854]  [<ffffffff81a3664a>] apic_timer_interrupt+0x6a/0x70
> [   38.615855]  <EOI>
> [   38.615861]  [<ffffffff810dc604>] ? __res_counter_charge+0xc4/0x170
> [   38.615866]  [<ffffffff81a34487>] ? _raw_spin_lock+0x47/0x60
> [   38.615882]  [<ffffffff81a34457>] ? _raw_spin_lock+0x17/0x60
> [   38.615885]  [<ffffffff810dc604>] __res_counter_charge+0xc4/0x170
> [   38.615888]  [<ffffffff810dc6c0>] res_counter_charge+0x10/0x20
> [   38.615896]  [<ffffffff81186645>] vm_cgroup_charge_shmem+0x35/0x50
> [   38.615900]  [<ffffffff8113a686>] shmem_getpage_gfp+0x4b6/0x8e0
> [   38.615904]  [<ffffffff8108201d>] ? get_parent_ip+0xd/0x50
> [   38.615908]  [<ffffffff8113b626>] shmem_symlink+0xe6/0x210
> [   38.615914]  [<ffffffff81195361>] ? __inode_permission+0x41/0xd0
> [   38.615917]  [<ffffffff811961f0>] vfs_symlink+0x90/0xd0
> [   38.615923]  [<ffffffff8119a762>] SyS_symlinkat+0x62/0xc0
> [   38.615927]  [<ffffffff8119a7d6>] SyS_symlink+0x16/0x20
> [   38.615930]  [<ffffffff81a359d6>] system_call_fastpath+0x1a/0x1f
> 
> 
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