linux-kernel - Re: [PATCH] x86: UV: raw

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Date:   Sat, 19 May 2018 16:09:56 +0200
From:   Mike Galbraith <gleep@....de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH] x86: UV: raw_spinlock conversion

On Mon, 2018-05-07 at 09:39 +0200, Sebastian Andrzej Siewior wrote:
> On 2018-05-06 12:59:19 [+0200], Mike Galbraith wrote:
> > On Sun, 2018-05-06 at 12:26 +0200, Thomas Gleixner wrote:
> > > On Fri, 4 May 2018, Sebastian Andrzej Siewior wrote:
> > > 
> > > > From: Mike Galbraith <umgwanakikbuti@...il.com>
> > > > 
> > > > Shrug.  Lots of hobbyists have a beast in their basement, right?
> > > 
> > > This hardly qualifies as a proper changelog ...
> > 
> > Hm, that wasn't intended to be a changelog.
> > 
> > This patch may not be current either, I haven't tested RT on a UV box
> > in quite some time.
> 
> That last hunk looks like something that would be required even for !RT. 
> Would you mind to check that patch and write a changelog? If it doesn't
> work for RT there is no need to carry this in -RT.

None of that patch is needed for a UV3000, but the below is.  It's
likely still valid for now ancient UV boxen, but the UV100 the patch
was originally written for (2011/2.6.33-rt) has apparently wandered off
to become a beer keg or something meanwhile, so I can't test.

UV: Fix uv_bau_init() check_preemption_disabled() gripeage

[    2.851947] BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
[    2.851951] caller is uv_bau_init+0x28/0xb62
[    2.851954] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.17.0-rc5-0.g3e3e37b-rt_debug
[    2.851956] Hardware name: SGI UV3000/UV3000, BIOS SGI UV 3000 series BIOS 01/15/2015
[    2.851957] Call Trace:
[    2.851964]  dump_stack+0x85/0xcb
[    2.851969]  check_preemption_disabled+0x10c/0x120
[    2.851972]  ? init_per_cpu+0x88c/0x88c
[    2.851974]  uv_bau_init+0x28/0xb62
[    2.851979]  ? lapic_cal_handler+0xbb/0xbb
[    2.851982]  ? rt_mutex_unlock+0x35/0x50
[    2.851985]  ? init_per_cpu+0x88c/0x88c
[    2.851988]  ? set_debug_rodata+0x11/0x11
[    2.851991]  do_one_initcall+0x46/0x249
[    2.851995]  kernel_init_freeable+0x207/0x29c
[    2.851999]  ? rest_init+0xd0/0xd0
[    2.852000]  kernel_init+0xa/0x110
[    2.852000]  ret_from_fork+0x3a/0x50

(gdb) list *uv_bau_init+0x28
0xffffffff824a4d96 is in uv_bau_init (./arch/x86/include/asm/uv/uv_hub.h:212).
207             return (struct uv_hub_info_s *)__uv_hub_info_list[node];
208     }
209
210     static inline struct uv_hub_info_s *_uv_hub_info(void)
211     {
212             return (struct uv_hub_info_s *)uv_cpu_info->p_uv_hub_info;
213     }
214     #define uv_hub_info     _uv_hub_info()
215
216     static inline struct uv_hub_info_s *uv_cpu_hub_info(int cpu)
(gdb)

arch/x86/include/asm/uv/uv_hub.h:
197 #define uv_cpu_info             this_cpu_ptr(&__uv_cpu_info)

This and other substitutions make uv_bau_init() annoying for a PREEMPT
kernel, but PREEMPT_RT can silence the lot with one migrate_disable().

Signed-off-by: Mike Galbraith <efault@....de>
---
 arch/x86/platform/uv/tlb_uv.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/platform/uv/tlb_uv.c
+++ b/arch/x86/platform/uv/tlb_uv.c
@@ -2213,6 +2213,8 @@ static int __init uv_bau_init(void)
 	if (!is_uv_system())
 		return 0;
 
+	migrate_disable();
+
 	if (is_uv4_hub())
 		ops = uv4_bau_ops;
 	else if (is_uv3_hub())
@@ -2269,6 +2271,8 @@ static int __init uv_bau_init(void)
 		}
 	}
 
+	migrate_enable();
+
 	return 0;
 
 err_bau_disable:
@@ -2276,6 +2280,7 @@ static int __init uv_bau_init(void)
 	for_each_possible_cpu(cur_cpu)
 		free_cpumask_var(per_cpu(uv_flush_tlb_mask, cur_cpu));
 
+	migrate_enable();
 	set_bau_off();
 	nobau_perm = 1;