linux-kernel - Re: [tip:perf/core] perf, trace: Fix IRQ-disable removal from perf/tracepoint interaction

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Message-ID: <1274778175.5882.623.camel@twins>
Date:	Tue, 25 May 2010 11:02:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	mingo@...hat.com, hpa@...or.com, paulus@...ba.org, acme@...hat.com,
	linux-kernel@...r.kernel.org, efault@....de, fweisbec@...il.com,
	rostedt@...dmis.org, tglx@...utronix.de, mingo@...e.hu
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf, trace: Fix IRQ-disable removal from
 perf/tracepoint interaction

On Tue, 2010-05-25 at 08:06 +0000, tip-bot for Peter Zijlstra wrote:
> Commit-ID:  23ef672d1e8236e6fe606a39963ba2d576972d84
> Gitweb:     http://git.kernel.org/tip/23ef672d1e8236e6fe606a39963ba2d576972d84
> Author:     Peter Zijlstra <peterz@...radead.org>
> AuthorDate: Sun, 23 May 2010 20:16:27 +0200
> Committer:  Ingo Molnar <mingo@...e.hu>
> CommitDate: Tue, 25 May 2010 09:02:08 +0200
> 
> perf, trace: Fix IRQ-disable removal from perf/tracepoint interaction
> 
> On x86 perf_arch_fetch_caller_regs() stores pt_regs::flags, which is the
> same as used in local_save_flags().
> 
> So to avoid another local_save_flags() for the ftrace code, I wanted to
> reuse it, and totally forgot the !x86 side of things.
> 
> [ Possibly we could remove the local_save_flags() from the
>   perf_arch_fetch_caller_regs() as I'm not sure we actually use
>   pt_regs::flags (Frederic?) and leave the ftrace thing to use
>   local_save_flags(). ]
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Acked-by: Paul Mackerras <paulus@...ba.org>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Mike Galbraith <efault@....de>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> LKML-Reference: <20100524042958.GA10628@...ngo>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>

Could you replace this with:


---
Subject: perf, trace: Fix !x86 build issue
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Tue May 25 09:22:38 CEST 2010

Patch b7e2ecef92 (perf, trace: Optimize tracepoints by removing
IRQ-disable from perf/tracepoint interaction) made the unfortunate
mistake of assuming the world is x86 only, correct this.

The problem was that perf_fetch_caller_regs() did local_save_flags()
into regs->flags, and I re-used that to remove another
local_save_flags(), forgetting !x86 doesn't have regs->flags.

Do the reverse, remove the local_save_flags() from
perf_fetch_caller_regs() and let the ftrace site do the
local_save_flags() instead.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Acked-by: Paul Mackerras <paulus@...ba.org>
---
 arch/x86/kernel/cpu/perf_event.c |    6 +++++-
 kernel/trace/trace_event_perf.c  |    4 +++-
 2 files changed, 8 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c
+++ linux-2.6/arch/x86/kernel/cpu/perf_event.c
@@ -1717,7 +1717,11 @@ void perf_arch_fetch_caller_regs(struct 
 	 */
 	regs->bp = rewind_frame_pointer(skip + 1);
 	regs->cs = __KERNEL_CS;
-	local_save_flags(regs->flags);
+	/*
+	 * We abuse bit 3 to pass exact information, see perf_misc_flags
+	 * and the comment with PERF_EFLAGS_EXACT.
+	 */
+	regs->flags = 0;
 }
 
 unsigned long perf_instruction_pointer(struct pt_regs *regs)
Index: linux-2.6/kernel/trace/trace_event_perf.c
===================================================================
--- linux-2.6.orig/kernel/trace/trace_event_perf.c
+++ linux-2.6/kernel/trace/trace_event_perf.c
@@ -157,6 +157,7 @@ __kprobes void *perf_trace_buf_prepare(i
 				       struct pt_regs *regs, int *rctxp)
 {
 	struct trace_entry *entry;
+	unsigned long flags;
 	char *raw_data;
 	int pc;
 
@@ -174,7 +175,8 @@ __kprobes void *perf_trace_buf_prepare(i
 	memset(&raw_data[size - sizeof(u64)], 0, sizeof(u64));
 
 	entry = (struct trace_entry *)raw_data;
-	tracing_generic_entry_update(entry, regs->flags, pc);
+	local_save_flags(flags);
+	tracing_generic_entry_update(entry, flags, pc);
 	entry->type = type;
 
 	return raw_data;

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