Re: [PATCH perf/core 00/22] perf refcnt debugger API and fixes

[Wangnan (F)]

On 2015/12/11 10:15, åæéå / HIRAMATUïMASAMI wrote:
> From: 'Arnaldo Carvalho de Melo' [mailto:acme@xxxxxxxxxx]
> > But this requires having these special refcnt__ routines, that will make
> > tools/perf/ code patterns for reference counts look different that the
> > refcount patterns in the kernel :-\
> BTW, I think even without the refcnt debugger, we'd better introduce this
> kind API to unify the refcnt operation in perf code. As I said, we have many
> miscodings on current implementation. Unifying the API can enforce developers
> to avoid such miscodings.
>
> Thank you,

I tried this problem in another way, I'd like to share it here.

First: create two uprobes:

# ./perf probe --exec /home/wangnan/perf dso__new%return %ax
Added new event:
  probe_perf:dso__new  (on dso__new%return in /home/wangnan/perf with %ax)

You can now use it in all perf tools, such as:

    perf record -e probe_perf:dso__new -aR sleep 1

# ./perf probe --exec /home/wangnan/perf dso__delete dso
Added new event:
  probe_perf:dso__delete (on dso__delete in /home/wangnan/perf with dso)

You can now use it in all perf tools, such as:

    perf record -e probe_perf:dso__delete -aR sleep 1


Then start test:

# ./perf record -g -e probe_perf:dso__new -e probe_perf:dso__delete 
./perf probe vfs_read
Added new event:
  probe:vfs_read       (on vfs_read)

You can now use it in all perf tools, such as:

    perf record -e probe:vfs_read -aR sleep 1

[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.048 MB perf.data (178 samples) ]


From the perf report result I know two dso objects are leak:

90 probe_perf:dso__new `
88 probe_perf:dso__delete


Then convert output to CTF:

$ ./perf data convert --to-ctf ./out.ctf


With a python script, try to find the exact leak objects (I'm not good 
at python,
I believe we can do this with much shorter script):

$ cat refcnt.py
from babeltrace import TraceCollection

tc = TraceCollection();
tc.add_trace('./out.ctf', 'ctf')
objs = {}
for event in tc.events:
    if event.name.startswith('probe_perf:dso__new'):
        if event['arg1'] not in objs:
            objs[event['arg1']] = 1
    if event.name.startswith('probe_perf:dso__delete'):
        if event['dso'] in objs:
            objs[event['dso']] = 0

for x in objs:
    if objs[x] is 0:
        continue
    print("0x%x" % x)

$ python3 ./refcnt.py
0x34cb350
0x34d4640

Then from perf script's result, search for the two address:

perf 23203 [004] 665244.170387: probe_perf:dso__new: (4aaee0 <- 50a5eb) 
arg1=0x34cb350
                  10a5eb dso__load_sym (/home/w00229757/perf)
                   af42d dso__load_vmlinux (/home/w00229757/perf)
                   af58c dso__load_vmlinux_path (/home/w00229757/perf)
                  10c40a open_debuginfo (/home/w00229757/perf)
                  111d39 convert_perf_probe_events (/home/w00229757/perf)
                   603a7 __cmd_probe.isra.3 (/home/w00229757/perf)
                   60a44 cmd_probe (/home/w00229757/perf)
                   7f6d1 run_builtin (/home/w00229757/perf)
                   33056 main (/home/w00229757/perf)
                   21bd5 __libc_start_main 
(/tmp/oxygen_root-w00229757/lib64/libc-2.18.so)

perf 23203 [004] 665244.170679: probe_perf:dso__new: (4aaee0 <- 50a5eb) 
arg1=0x34d4640
                  10a5eb dso__load_sym (/home/w00229757/perf)
                   af42d dso__load_vmlinux (/home/w00229757/perf)
                   af58c dso__load_vmlinux_path (/home/w00229757/perf)
                  10c40a open_debuginfo (/home/w00229757/perf)
                  111d39 convert_perf_probe_events (/home/w00229757/perf)
                   603a7 __cmd_probe.isra.3 (/home/w00229757/perf)
                   60a44 cmd_probe (/home/w00229757/perf)
                   7f6d1 run_builtin (/home/w00229757/perf)
                   33056 main (/home/w00229757/perf)
                   21bd5 __libc_start_main 
(/tmp/oxygen_root-w00229757/lib64/libc-2.18.so)

Thank you.

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