Em Sat, Apr 25, 2015 at 07:25:03AM +0000, Wang Nan escreveu:
> Perf top raise a warning if a kernel sample is collected but kernel map
> is restricted. The warning message needs to dereference al.map->dso...
> However, previous perf_event__preprocess_sample() doesn't always
> guarantee al.map != NULL, for example, when kernel map is restricted.
>
> This patch validates al.map before dereferencing, avoid the segfault.
>
> Before this patch:
>
> $ cat /proc/sys/kernel/kptr_restrict
> 1
> $ perf top -p 120183
> perf: Segmentation fault
> -------- backtrace --------
> /path/to/perf[0x509868]
> /lib64/libc.so.6(+0x3545f)[0x7f9a1540045f]
> /path/to/perf[0x448820]
> /path/to/perf(cmd_top+0xe3c)[0x44a5dc]
> /path/to/perf[0x4766a2]
> /path/to/perf(main+0x5f5)[0x42e545]
> /lib64/libc.so.6(__libc_start_main+0xf4)[0x7f9a153ecbd4]
> /path/to/perf[0x42e674]
Thanks for the detailed report, I reproduced the problem here and I am
applying the patch.
- Arnaldo
> And gdb call trace:
>
> Program received signal SIGSEGV, Segmentation fault.
> perf_event__process_sample (machine=0xa44030, sample=0x7fffffffa4c0,
> evsel=0xa43b00, event=0x7ffff41c3000, tool=0x7fffffffa8a0)
> at builtin-top.c:736
> 736
> !RB_EMPTY_ROOT(&al.map->dso->symbols[MAP__FUNCTION]) ?
> (gdb) bt
> #0 perf_event__process_sample (machine=0xa44030, sample=0x7fffffffa4c0,
> evsel=0xa43b00, event=0x7ffff41c3000, tool=0x7fffffffa8a0)
> at builtin-top.c:736
> #1 perf_top__mmap_read_idx (top=top@entry=0x7fffffffa8a0, idx=idx@entry=0)
> at builtin-top.c:855
> #2 0x000000000044a5dd in perf_top__mmap_read (top=0x7fffffffa8a0) at
> builtin-top.c:872
> #3 __cmd_top (top=0x7fffffffa8a0) at builtin-top.c:997
> #4 cmd_top (argc=<optimized out>, argv=<optimized out>, prefix=<optimized
> out>) at builtin-top.c:1267
> #5 0x00000000004766a3 in run_builtin (p=p@entry=0x8a6ce8 <commands+264>,
> argc=argc@entry=3, argv=argv@entry=0x7fffffffdf70)
> at perf.c:371
> #6 0x000000000042e546 in handle_internal_command (argv=0x7fffffffdf70,
> argc=3) at perf.c:430
> #7 run_argv (argv=0x7fffffffdcf0, argcp=0x7fffffffdcfc) at perf.c:474
> #8 main (argc=3, argv=0x7fffffffdf70) at perf.c:589
> (gdb)
>
> Signed-off-by: Wang Nan <wangn...@huawei.com>
> ---
>
> I don't receive previous mail from the list so send it again.
>
> ---
>
> tools/perf/builtin-top.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index 1cb3436..6a4d5d4 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -733,7 +733,7 @@ static void perf_event__process_sample(struct perf_tool
> *tool,
> "Kernel address maps (/proc/{kallsyms,modules}) are restricted.\n\n"
> "Check /proc/sys/kernel/kptr_restrict.\n\n"
> "Kernel%s samples will not be resolved.\n",
> - !RB_EMPTY_ROOT(&al.map->dso->symbols[MAP__FUNCTION]) ?
> + al.map &&
> !RB_EMPTY_ROOT(&al.map->dso->symbols[MAP__FUNCTION]) ?
> " modules" : "");
> if (use_browser <= 0)
> sleep(5);
> --
> 1.8.3.4
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