Messages in this thread | | | Subject | Re: [PATCH 1/2] perf tools: Fix seg fault with Intel PT | From | Adrian Hunter <> | Date | Tue, 26 Jan 2016 16:00:56 +0200 |
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On 26/01/16 15:54, Arnaldo Carvalho de Melo wrote: > Em Tue, Jan 26, 2016 at 03:34:15PM +0200, Adrian Hunter escreveu: >> On 26/01/16 15:23, Arnaldo Carvalho de Melo wrote: >>> Em Tue, Jan 26, 2016 at 02:05:20PM +0200, Adrian Hunter escreveu: >>>> Fix segmentation fault using: >>>> >>>> perf record -e intel_pt//u uname >>>> >>>> Back trace: >>>> >>>> 0 tracepoint_error (err=13, err@entry=-13, sys=sys@entry=0x18706c0 "sched", name=name@entry=0x1871c70 "sched_switch", e=<optimized out>, e=<optimized out>) at util/parse-events.c:416 >>>> 1 0x000000000049791c in add_tracepoint (head_config=0x0, err=0x0, evt_name=0x1871c70 "sched_switch", sys_name=0x18706c0 "sched", idx=<optimized out>, list=<optimized out>) >>>> at util/parse-events.c:433 >>>> 2 add_tracepoint_event (list=<optimized out>, idx=<optimized out>, sys_name=0x18706c0 "sched", evt_name=0x1871c70 "sched_switch", err=0x0, head_config=0x0) at util/parse-events.c:498 >>>> 3 0x0000000000498ec4 in parse_events_add_tracepoint (list=list@entry=0x1871c90, idx=idx@entry=0x7fffffffba30, sys=0x18706c0 "sched", event=0x1871c70 "sched_switch", err=err@entry=0x0, >>>> head_config=head_config@entry=0x0) at util/parse-events.c:936 >>>> 4 0x00000000004ccff2 in parse_events_parse (_data=_data@entry=0x7fffffffba20, scanner=0x18705f0) at util/parse-events.y:391 >>>> 5 0x000000000049a567 in parse_events__scanner (start_token=258, data=0x7fffffffba20, str=0x0) at util/parse-events.c:1361 >>>> 6 parse_events (evlist=evlist@entry=0x1871150, str=str@entry=0x55ef6c "sched:sched_switch", err=err@entry=0x0) at util/parse-events.c:1401 >>>> 7 0x00000000004eb4b6 in perf_evlist__can_select_event (evlist=evlist@entry=0x186fb90, str=str@entry=0x55ef6c "sched:sched_switch") at util/record.c:253 >>>> 8 0x000000000051e1d3 in intel_pt_track_switches (evlist=0x186fb90) at arch/x86/util/intel-pt.c:362 >>>> 9 intel_pt_recording_options (itr=0x186ef70, evlist=0x186fb90, opts=0x7c3e08 <record+232>) at arch/x86/util/intel-pt.c:662 >>>> 10 0x000000000042e244 in cmd_record (argc=1, argv=0x7fffffffe270, prefix=<optimized out>) at builtin-record.c:1260 >>>> 11 0x000000000047cbd3 in run_builtin (p=p@entry=0x7cf2e8 <commands+168>, argc=argc@entry=4, argv=argv@entry=0x7fffffffe270) at perf.c:390 >>>> 12 0x00000000004216a7 in handle_internal_command (argv=0x7fffffffe270, argc=4) at perf.c:451 >>>> 13 run_argv (argv=0x7fffffffdff0, argcp=0x7fffffffdffc) at perf.c:495 >>>> 14 main (argc=4, argv=0x7fffffffe270) at perf.c:618 >>>> >>>> Intel PT attempts to find the sched:sched_switch tracepoint but that >>>> seg faults if tracefs is not readable, because the error reporting >>> >>> How can I reproduce this problem? I tried your command but that doesn't cause >>> any problem: >>> >>> [acme@jouet linux]$ ls -la /sys/kernel/debug/tracing/ >>> ls: cannot access /sys/kernel/debug/tracing/: Permission denied >>> [acme@jouet linux]$ ls -la /sys/kernel/debug/ >>> ls: cannot open directory /sys/kernel/debug/: Permission denied >>> [acme@jouet linux]$ perf record -e intel_pt//u uname >>> Linux >>> [ perf record: Woken up 1 times to write data ] >>> [ perf record: Captured and wrote 0.041 MB perf.data ] >>> [acme@jouet linux]$ perf list intel >>> >>> List of pre-defined events (to be used in -e): >>> >>> intel_bts// [Kernel PMU event] >>> intel_pt// [Kernel PMU event] >>> >>> [acme@jouet linux]$ perf record -e intel_pt//u uname >>> Linux >>> [ perf record: Woken up 1 times to write data ] >>> [ perf record: Captured and wrote 0.041 MB perf.data ] >>> [acme@jouet linux]$ >>> >>> [acme@jouet linux]$ perf evlist >>> intel_pt//u >>> dummy:u >>> [acme@jouet linux]$ >>> >>> [acme@jouet linux]$ perf evlist -v >>> intel_pt//u: type: 6, size: 112, config: 0x400, { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CPU|IDENTIFIER, read_format: ID, disabled: 1, inherit: 1, exclude_kernel: 1, exclude_hv: 1, enable_on_exec: 1, sample_id_all: 1 >>> dummy:u: type: 1, size: 112, config: 0x9, { sample_period, sample_freq }: 1, sample_type: IP|TID|TIME|CPU|IDENTIFIER, read_format: ID, disabled: 1, inherit: 1, exclude_kernel: 1, exclude_hv: 1, mmap: 1, comm: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, mmap2: 1, comm_exec: 1, context_switch: 1 >>> [acme@jouet linux]$ >>> >>> Humm, ok, so this happens only if tracefs is not readable _and_ this is an >>> older kernel where perf_event_attr.context_switch is not available? >> >> Yes, I should have thought of that, sorry. > > So, I just tried on another machine, with an older kernel > > [acme@ssdandy linux]$ uname -r > 3.10.0-229.14.1.el7.x86_64 > [acme@ssdandy linux]$ ls -la /sys/kernel/debug/ > ls: cannot open directory /sys/kernel/debug/: Permission denied > [acme@ssdandy linux]$ > [acme@ssdandy linux]$ grep tracefs /proc/filesystems > [acme@ssdandy linux]$ grep debugfs /proc/filesystems > nodev debugfs > [acme@ssdandy linux]$ ls -la /sys/kernel/debug/ > ls: cannot open directory /sys/kernel/debug/: Permission denied > [acme@ssdandy linux]$ perf record -e intel_pt//u uname > invalid or unsupported event: 'intel_pt//u' > Run 'perf list' for a list of valid events > > Usage: perf record [<options>] [<command>] > or: perf record [<options>] -- <command> [<options>] > > -e, --event <event> event selector. use 'perf list' to list available events > [acme@ssdandy linux]$ > > So, this needs: > > 1) A machine that supports Intel PT > 2) A kernel that supports Intel PT > 3) A kernel that doesn't have perf_event_attr.context_switch, so that it tries > to use sched:sched_switch > 4) an unreadable tracefs > > What was the kernel where you stumbled on this problem? What machine?
Kernel was v4.2, machine was Broadwell.
context_switch was added in v4.3 I think, and PT was v4.1 so I guess v4.1 and v4.2 are affected.
> > - Arnaldo > >>> /me tries booting another machine, with an older kernel... >>> >>>> structure is null, as errors are not reported when automatically >>>> adding tracepoints. Fix by checking before using. >>>> >>>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> >>>> Fixes: 196581717d85 ("perf tools: Enhance parsing events tracepoint error output") >>>> Cc: stable@vger.kernel.org # v4.4+ >>>> --- >>>> tools/perf/util/parse-events.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c >>>> index 4f7b0efdde2f..813d9b272c81 100644 >>>> --- a/tools/perf/util/parse-events.c >>>> +++ b/tools/perf/util/parse-events.c >>>> @@ -399,6 +399,9 @@ static void tracepoint_error(struct parse_events_error *e, int err, >>>> { >>>> char help[BUFSIZ]; >>>> >>>> + if (!e) >>>> + return; >>>> + >>>> /* >>>> * We get error directly from syscall errno ( > 0), >>>> * or from encoded pointer's error ( < 0). >>>> -- >>>> 1.9.1 >>> >
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