Re: [BUG] perf top -G is broken

[Arnaldo Carvalho de Melo <acme@ghostprotocols.net>]

Em Fri, May 04, 2012 at 03:55:34PM -0600, David Ahern escreveu:
> On 5/3/12 10:09 PM, Namhyung Kim wrote:
> >Hi,
> >
> >On Wed, 2 May 2012 13:02:50 -0300, Arnaldo Carvalho de Melo wrote:
> >>Em Wed, May 02, 2012 at 11:50:45AM +0900, Namhyung Kim escreveu:
> >>>Some guy reported me that perf top -G is broken with segment fault. I
> >>>can reproduce it on my system easily but the time is vary - few seconds
> >>>to 30 minutes. I ran it with --stdio to get a core file:
> >>
> >>Does it help to increase --mmap-pages from its default, 128, to
> >>something like 512 or more?
> >>
> >>Also try running with -r 90.
> >>
> >>- Arnaldo
> >
> >Testing both options with current tip/perf/core gives me the same result. :(
> 
> Have a few minutes before catching a plane. Running 'hackbench 10
> thread 4000' in a loop in one window and perf top -G within gdb in
> another (tip/perf/core as of today):
> 
> (gdb) info thr
>   Id   Target Id         Frame
> * 2    Thread 0x7ffff0407700 (LWP 1109) "perf" 0x00000000004575c6 in
> callchain_cursor_advance (cursor=<optimized out>)
>     at util/callchain.h:141
>   1    Thread 0x7ffff7fd7940 (LWP 925) "perf" 0x00007ffff35ff819 in
> calloc () from /lib64/libc.so.6
> 
> (gdb) bt
> #0  0x00000000004575c6 in callchain_cursor_advance
> (cursor=<optimized out>) at util/callchain.h:141
> #1  fill_node (node=0x7fffe8293e80, cursor=0x8e4f58) at util/callchain.c:226
> #2  0x0000000000458f80 in add_child (period=2719949,
> cursor=0x8e4f58, parent=0xc8e110) at util/callchain.c:239
> #3  append_chain_children (period=2719949, cursor=0x8e4f58,
> root=0xc8e110) at util/callchain.c:308
> #4  merge_chain_branch (cursor=0x8e4f58, dst=0xc8e110,
> src=0x10462f0) at util/callchain.c:415
> #5  0x0000000000458e9a in merge_chain_branch (cursor=0x8e4f58,
> dst=0xc8e110, src=0xfdabf0) at util/callchain.c:419
> #6  0x0000000000473ef8 in hists__collapse_insert_entry (he=0xfdab40,
> root=0x8e4da0, hists=0x8e4d80) at util/hist.c:401
> #7  __hists__collapse_resort (hists=0x8e4d80, threaded=<optimized
> out>) at util/hist.c:458
> #8  0x0000000000426563 in perf_top__print_sym_table
> (top=0x7fffffffd530) at builtin-top.c:309
> #9  display_thread (arg=0x7fffffffd530) at builtin-top.c:623
> #10 0x00007ffff7bc6d90 in start_thread () from /lib64/libpthread.so.0
> #11 0x00007ffff366cf5d in clone () from /lib64/libc.so.6
> 
> (gdb) thr 1
> [Switching to thread 1 (Thread 0x7ffff7fd7940 (LWP 925))]
> #0  0x00007ffff35ff819 in calloc () from /lib64/libc.so.6
> 
> (gdb) bt
> #0  0x00007ffff35ff819 in calloc () from /lib64/libc.so.6
> #1  0x000000000045758f in zalloc (size=48) at util/util.h:183
> #2  fill_node (node=0xf15710, cursor=0x8e4f58) at util/callchain.c:216
> #3  0x0000000000459159 in add_child (period=2655425,
> cursor=0x8e4f58, parent=0x104a680) at util/callchain.c:239
> #4  append_chain_children (period=2655425, cursor=0x8e4f58,
> root=0x104a680) at util/callchain.c:308
> #5  callchain_append (root=0x104a678, cursor=0x8e4f58,
> period=2655425) at util/callchain.c:388
> #6  0x00000000004255df in perf_event__process_sample
> (machine=<optimized out>, sample=0x7fffffffd440, evsel=0x8e4cf0,
>     event=<optimized out>, tool=0x7fffffffd530) at builtin-top.c:790
> #7  perf_top__mmap_read_idx (top=0x7fffffffd530, idx=2) at builtin-top.c:858
> #8  0x0000000000427607 in perf_top__mmap_read (top=0x7fffffffd530)
> at builtin-top.c:873
> #9  __cmd_top (top=0x7fffffffd530) at builtin-top.c:1054
> #10 cmd_top (argc=<optimized out>, argv=<optimized out>,
> prefix=<optimized out>) at builtin-top.c:1333
> #11 0x0000000000414403 in run_builtin (p=0x774448, argc=3,
> argv=0x7fffffffe320) at perf.c:273
> #12 0x0000000000413c31 in handle_internal_command
> (argv=0x7fffffffe320, argc=3) at perf.c:345
> #13 run_argv (argv=0x7fffffffe130, argcp=0x7fffffffe13c) at perf.c:389
> #14 main (argc=3, argv=0x7fffffffe320) at perf.c:487
> 
> Cross thread corruption. Both threads are operating on the cursor at
> 0x8e4f58 in this example.

Thanks for the clue! Namhyung, have you used this info or did you
indepently figure this out?

No offense intended, just trying to get some sort of stimulus package
right :-P

- Arnaldo