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

Peter Zijlstra
2010-05-25T09:03:24Z

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@infradead.org>
> AuthorDate: Sun, 23 May 2010 20:16:27 +0200
> Committer: Ingo Molnar <mingo@elte.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@chello.nl>
> Acked-by: Paul Mackerras <paulus@samba.org>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Mike Galbraith <efault@gmx.de>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> LKML-Reference: <20100524042958.GA10628@drongo>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>

Could you replace this with:

---
Subject: perf, trace: Fix !x86 build issue
From: Peter Zijlstra <a.p.zijlstra@chello.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@chello.nl>
Acked-by: Paul Mackerras <paulus@samba.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;