linux-kernel - [PATCH] perf kvm: fix regression with guest machine creation

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Date:	Sun,  1 Jul 2012 16:11:37 -0600
From:	David Ahern <dsahern@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	psuriset@...ux.vnet.ibm.com, David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] perf kvm: fix regression with guest machine creation

Commit 743eb868657bdb1b26c7b24077ca21c67c82c777 reworked when the
machines were created. Prior to this commit guest machines could be
created in perf_event__process_kernel_mmap() while processing
kernel MMAP events. This commit assumes that the machines exist by
the time perf_session_deliver_event is called (e.g., during
processing of build id events) - which is not always correct.

One example is the use of default guest args (--guestkallsyms
and --guestmodules) for short times where no samples hit within
a guest module. For this case no build id is added to the file
header. No build id == no machine created. That leads to the next
example -- the use of no-buildid (-B) on the record for all
perf-kvm invocations. In both cases perf report dies with a
SEGFAULT of the form:

(gdb) bt
0  0x000000000046dd7b in machine__mmap_name (self=0x0, bf=0x7fffffffbd20 "q\021", size=4096) at util/map.c:715
1  0x0000000000444161 in perf_event__process_kernel_mmap (tool=0x7fffffffdd80, event=0x7ffff7fb4120, machine=0x0) at util/event.c:562
2  0x0000000000444642 in perf_event__process_mmap (tool=0x7fffffffdd80, event=0x7ffff7fb4120, sample=0x7fffffffd210, machine=0x0)
    at util/event.c:668
3  0x0000000000470e0b in perf_session_deliver_event (session=0x915ca0, event=0x7ffff7fb4120, sample=0x7fffffffd210, tool=0x7fffffffdd80,
    file_offset=8480) at util/session.c:979
4  0x000000000047032e in flush_sample_queue (s=0x915ca0, tool=0x7fffffffdd80) at util/session.c:679
5  0x0000000000471c8d in __perf_session__process_events (session=0x915ca0, data_offset=400, data_size=150448, file_size=150848, tool=
    0x7fffffffdd80) at util/session.c:1363
6  0x0000000000471d42 in perf_session__process_events (self=0x915ca0, tool=0x7fffffffdd80) at util/session.c:1379
7  0x000000000042484a in __cmd_report (rep=0x7fffffffdd80) at builtin-report.c:368
8  0x0000000000425bf1 in cmd_report (argc=0, argv=0x915b00, prefix=0x0) at builtin-report.c:756
9  0x0000000000438505 in __cmd_report (argc=4, argv=0x7fffffffe260) at builtin-kvm.c:84
10 0x000000000043882a in cmd_kvm (argc=4, argv=0x7fffffffe260, prefix=0x0) at builtin-kvm.c:131
11 0x00000000004152cd in run_builtin (p=0x7a54e8, argc=9, argv=0x7fffffffe260) at perf.c:273
12 0x00000000004154c7 in handle_internal_command (argc=9, argv=0x7fffffffe260) at perf.c:345
13 0x0000000000415613 in run_argv (argcp=0x7fffffffe14c, argv=0x7fffffffe140) at perf.c:389
14 0x0000000000415899 in main (argc=9, argv=0x7fffffffe260) at perf.c:487

Fix by allowing the machine to be created in perf_session_deliver_event.

Tested with --guestmount option and default guest args, with and without
-B arg on record for both and for short (10 seconds) and long (10 minutes)
windows.

Reported-by: Pradeep Kumar Surisetty <psuriset@...ux.vnet.ibm.com>
CC: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...il.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: David Ahern <dsahern@...il.com>
---
 tools/perf/util/session.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index c3e399b..56142d0 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -926,7 +926,7 @@ static struct machine *
 		else
 			pid = event->ip.pid;
 
-		return perf_session__find_machine(session, pid);
+		return perf_session__findnew_machine(session, pid);
 	}
 
 	return perf_session__find_host_machine(session);
-- 
1.7.10.1

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