Re: [PATCH] perf/x86/intel/cqm: Move WARN_ONs from intel_cqm_cpu_prepare to cqm_pick_event_reader

Matt Fleming
2015-08-12T11:00:30Z

On Tue, 11 Aug, at 01:31:05PM, Yasuaki Ishimatsu wrote:
> When hot adding a CPU and onlining it, the following WARN_ON() messages
> are shown:
>
> [ 772.891448] ------------[ cut here ]------------
> [ 772.896624] WARNING: CPU: 58 PID: 15169 at arch/x86/kernel/cpu/perf_event_intel_cqm.c:1268 intel_cqm_cpu_prepare+0x88/0x90()
> [ 772.909167] Modules linked in:
> [ 772.995134] CPU: 58 PID: 15169
> [ 773.016633] 0000000000000000 0000000092fb60ed ffff88104febbba8 ffffffff8167b5fa
> [ 773.024789] 0000000000000000 0000000000000000 ffff88104febbbe8 ffffffff810819ea
> [ 773.033119] ffff88103be60000 ffff8c0fbc7ca020 ffffffff819fadf0 000000000000008f
> [ 773.041461] Call Trace:
> [ 773.044402] [<ffffffff8167b5fa>] dump_stack+0x45/0x57
> [ 773.050160] [<ffffffff810819ea>] warn_slowpath_common+0x8a/0xc0
> [ 773.056888] [<ffffffff81081b1a>] warn_slowpath_null+0x1a/0x20
> [ 773.063426] [<ffffffff810365f8>] intel_cqm_cpu_prepare+0x88/0x90
> [ 773.070253] [<ffffffff81036732>] intel_cqm_cpu_notifier+0x42/0x160
> [ 773.077271] [<ffffffff810a0d3d>] notifier_call_chain+0x4d/0x80
> [ 773.083901] [<ffffffff810a0e4e>] __raw_notifier_call_chain+0xe/0x10
> [ 773.091007] [<ffffffff81081ef8>] _cpu_up+0xe8/0x190
> [ 773.096555] [<ffffffff8108201a>] cpu_up+0x7a/0xa0
> [ 773.101910] [<ffffffff816701b0>] cpu_subsys_online+0x40/0x90
> [ 773.108332] [<ffffffff8143d777>] device_online+0x67/0x90
> [ 773.114368] [<ffffffff8143d82a>] online_store+0x8a/0xa0
> [ 773.120305] [<ffffffff8143aab8>] dev_attr_store+0x18/0x30
> [ 773.126437] [<ffffffff8127224a>] sysfs_kf_write+0x3a/0x50
> [ 773.132560] [<ffffffff812718d0>] kernfs_fop_write+0x120/0x170
> [ 773.139078] [<ffffffff811f7657>] __vfs_write+0x37/0x100
> [ 773.145019] [<ffffffff811fa398>] ? __sb_start_write+0x58/0x110
> [ 773.151635] [<ffffffff8129d7ed>] ? security_file_permission+0x3d/0xc0
> [ 773.158932] [<ffffffff811f7d59>] vfs_write+0xa9/0x190
> [ 773.164674] [<ffffffff810234e6>] ? do_audit_syscall_entry+0x66/0x70
> [ 773.171776] [<ffffffff811f8b55>] SyS_write+0x55/0xc0
> [ 773.177423] [<ffffffff810672f0>] ? do_page_fault+0x30/0x80
> [ 773.183654] [<ffffffff8168232e>] entry_SYSCALL_64_fastpath+0x12/0x71
> [ 773.190843] ---[ end trace e6219d24386873bd ]---
> [ 773.196573] smpboot: Booting Node 7 Processor 143 APIC 0x1f7
> [ 773.221241] microcode: CPU143 sig=0x306f3, pf=0x80, revision=0x9
> [ 773.228005] Will online and init hotplugged CPU: 143
>
> Here is the root cause of the issue:
> When calling intel_cqm_cpu_prepare() at CPU_UP_PREPARE notification,
> the function checks that c86_chache_max_rmid is same as cqm_max_rmid
> as follows:
>
> static void intel_cqm_cpu_prepare(unsigned int cpu)
> {
> ...
> WARN_ON(c->x86_cache_max_rmid != cqm_max_rmid);
>
> But x86_cache_max_rmid of hot added CPU is not set yet, because it will
> set in get_cpu_cap() which is called after CPU_UP_PREPARE notification.
>
> So when onlining a hot added CPU, the WARN_ON() are always shown:

Thanks for the report! I submitted the following patch on August 6th to
fix this issue,

https://lkml.kernel.org/r/1438863163-14083-1-git-send-email-matt@codeblueprint.co.uk

> To fix the issue, the patch moves WARN_ON()s from intel_cqm_cpu_prepare() to
> cqm_pick_event_reader() which is called at CPU_STARTING notification.

I took a different approach and moved the notifier from CPU_UP_PREPARE
to CPU_STARTING since there's no reason to call the handler as early as
CPU_UP_PREPARE time at all.

Yes, we could collapse cqm_pick_event_reader() and
intel_cqm_cpu_prepare() together but I have a patch to add a
CPU_DOWN_FAILED call that invokes cqm_pick_event_reader() but not
intel_cqm_cpu_prepare(). I actually need to mail that out.

--
Matt Fleming, Intel Open Source Technology Center