perf record: Fix crash when kptr is restricted

Before this patch, a simple 'perf record' could fail if kptr_restrict is
set to 1 (for normal user) or 2 (for root):

  # perf record ls
  WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted,
  check /proc/sys/kernel/kptr_restrict.

  Samples in kernel functions may not be resolved if a suitable vmlinux
  file is not found in the buildid cache or in the vmlinux path.

  Samples in kernel modules won't be resolved at all.

  If some relocation was applied (e.g. kexec) symbols may be misresolved
  even with a suitable vmlinux or kallsyms file.

  Segmentation fault (core dumped)

This patch skips perf_event__synthesize_kernel_mmap() when kptr is not
available.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Fixes: 45e90056904b ("perf machine: Do not bail out if not managing to read ref reloc symbol")
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1464081688-167940-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index f6fcc68329499f255ddc1a5012dd36fdc04d8024..9b141f12329edc750de5eefd47c3c7f2cb46e503 100644 (file)
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -673,6 +673,8 @@ int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
        int err;
        union perf_event *event;
 
+       if (symbol_conf.kptr_restrict)
+               return -1;
        if (map == NULL)
                return -1;