linux-kernel - Re: [RFC][PATCH 4/7] perf: Fix scaling vs enable_on

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Message-ID: <20160226022512.GA29896@redhat.com>
Date:	Fri, 26 Feb 2016 03:25:12 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	alexander.shishkin@...ux.intel.com, eranian@...gle.com,
	linux-kernel@...r.kernel.org, vince@...ter.net, dvyukov@...gle.com,
	andi@...stfloor.org, sasha.levin@...cle.com,
	Pratyush Anand <panand@...hat.com>
Subject: Re: [RFC][PATCH 4/7] perf: Fix scaling vs enable_on_exec

On 02/23, Jiri Olsa wrote:
>
> so I finally got some reasonable backtrace and figured that crash finally:
>
>  #7 [ffff8802751afcd0] general_protection at ffffffff817a69e8
>     [exception RIP: special_mapping_fault+47]
>     RIP: ffffffff811e40df  RSP: ffff8802751afd88  RFLAGS: 00010282
>     RAX: ffff8802747e8b68  RBX: 00007fffffffe080  RCX: c4712d0070657267
>     RDX: ffff8802751afd98  RSI: ffff8802742c4f00  RDI: ffff8802747e8b68
>     RBP: ffff8802751afd88   R8: 0000000000000000   R9: ffff8802751afe58
>     R10: 00000000000001fe  R11: 00003fffffe00000  R12: ffff8802742c4f00
>     R13: ffff8802751afe58  R14: 0000000000000000  R15: ffff880273f59ff8
>     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
>  #8 [ffff8802751afd90] __do_fault at ffffffff811db505
>  #9 [ffff8802751afdf8] handle_mm_fault at ffffffff811e0b03
> #10 [ffff8802751afec8] __do_page_fault at ffffffff8106734a
> #11 [ffff8802751aff20] do_page_fault at ffffffff810675df
> #12 [ffff8802751aff50] page_fault at ffffffff817a6a48
>
>
> it was caused by:
>   - f872f5400cc0 mm: Add a vm_special_mapping.fault() method
>     that added call of vm_special_mapping::fault if it's defined

I guess it came from tip/x86...

>   - and uprobes code not initializing this fault pointer properly,
>     attached patch fixed the issue for me,
>     Oleg, I'm not sure this is how you want to fix this though..

Thanks! I'll send a simple fix tomorrow.

Oleg.