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[GIT PULL 0/2] perf/urgent fixes

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  [GIT PULL 0/2] perf/urgent fixes Arnaldo Carvalho de Melo <acme@kernel.org> - 2015-09-22 17:30 +0200
    [PATCH 1/2] perf record: Avoid infinite loop at buildid processing with no samples Arnaldo Carvalho de Melo <acme@kernel.org> - 2015-09-22 17:30 +0200
    Re: [GIT PULL 0/2] perf/urgent fixes Ingo Molnar <mingo@kernel.org> - 2015-09-23 09:50 +0200

#1230323 — [GIT PULL 0/2] perf/urgent fixes

Hi Ingo,

	Please consider pulling,

- Arnaldo

The following changes since commit f73e22ab450140830005581c2c7ec389791a1b8d:

  perf: Fix races in computing the header sizes (2015-09-18 09:20:26 +0200)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git tags/perf-urgent-for-mingo

for you to fetch changes up to c2e4b24ff848bb180f9b9cd873a38327cd219ad2:

  tools lib traceevent: Fix string handling in heterogeneous arch environments (2015-09-22 11:57:04 -0300)

----------------------------------------------------------------
perf/urgent fixes:

User visible:

- Fix libtraceevent string handling in heterogeneous arch environments (Kapileshwar Singh)

- Avoid infinite loop at buildid processing with no samples in 'perf record' (Mark Rutland)

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

----------------------------------------------------------------
Kapileshwar Singh (1):
      tools lib traceevent: Fix string handling in heterogeneous arch environments

Mark Rutland (1):
      perf record: Avoid infinite loop at buildid processing with no samples

 tools/lib/traceevent/event-parse.c | 23 ++++++++++++++++++++---
 tools/perf/util/session.c          |  5 ++++-
 2 files changed, 24 insertions(+), 4 deletions(-)
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#1230335 — [PATCH 1/2] perf record: Avoid infinite loop at buildid processing with no samples

From: Mark Rutland <mark.rutland@arm.com>

If a session contains no events, we can get stuck in an infinite loop in
__perf_session__process_events, with a non-zero file_size and data_offset, but
a zero data_size.

In this case, we can mmap the entirety of the file (consisting of the file and
attribute headers), and fetch_mmaped_event will correctly refuse to read any
(unmapped and non-existent) event headers. This causes
__perf_session__process_events to unmap the file and retry with the exact same
parameters, getting stuck in an infinite loop.

This has been observed to result in an exit-time hang when counting
rare/unschedulable events with perf record, and can be triggered artificially
with the script below:

  ----
  #!/bin/sh
  printf "REPRO: launching perf\n";
  ./perf record -e software/config=9/ sleep 1 &
  PERF_PID=$!;
  sleep 0.002;
  kill -2 $PERF_PID;
  printf "REPRO: waiting for perf (%d) to exit...\n" "$PERF_PID";
  wait $PERF_PID;
  printf "REPRO: perf exited\n";
  ----

To avoid this, have __perf_session__process_events bail out early when
the file has no data (i.e. it has no events).

Commiter note:

I only managed to reproduce this when setting
/proc/sys/kernel/kptr_restrict to '1' and changing the code to
purposefully not process any samples and no synthesized samples, i.e.
kptr_restrict prevents 'record' from synthesizing the kernel mmaps for
vmlinux + modules and since it is a workload started from perf, we don't
synthesize mmap/comm records for existing threads.

Adrian Hunter managed to reproduce it in his environment tho.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Tested-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1442423929-12253-1-git-send-email-mark.rutland@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/session.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 8a4537ee9bc3..fc3f7c922f99 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1580,7 +1580,10 @@ static int __perf_session__process_events(struct perf_session *session,
 	file_offset = page_offset;
 	head = data_offset - page_offset;
 
-	if (data_size && (data_offset + data_size < file_size))
+	if (data_size == 0)
+		goto out;
+
+	if (data_offset + data_size < file_size)
 		file_size = data_offset + data_size;
 
 	ui_progress__init(&prog, file_size, "Processing events...");
-- 
2.1.0

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#1231206

* Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Hi Ingo,
> 
> 	Please consider pulling,
> 
> - Arnaldo
> 
> The following changes since commit f73e22ab450140830005581c2c7ec389791a1b8d:
> 
>   perf: Fix races in computing the header sizes (2015-09-18 09:20:26 +0200)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git tags/perf-urgent-for-mingo
> 
> for you to fetch changes up to c2e4b24ff848bb180f9b9cd873a38327cd219ad2:
> 
>   tools lib traceevent: Fix string handling in heterogeneous arch environments (2015-09-22 11:57:04 -0300)
> 
> ----------------------------------------------------------------
> perf/urgent fixes:
> 
> User visible:
> 
> - Fix libtraceevent string handling in heterogeneous arch environments (Kapileshwar Singh)
> 
> - Avoid infinite loop at buildid processing with no samples in 'perf record' (Mark Rutland)
> 
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> ----------------------------------------------------------------
> Kapileshwar Singh (1):
>       tools lib traceevent: Fix string handling in heterogeneous arch environments
> 
> Mark Rutland (1):
>       perf record: Avoid infinite loop at buildid processing with no samples
> 
>  tools/lib/traceevent/event-parse.c | 23 ++++++++++++++++++++---
>  tools/perf/util/session.c          |  5 ++++-
>  2 files changed, 24 insertions(+), 4 deletions(-)

Pulled, thanks Arnaldo!

	Ingo
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