tracing/stack-tracer: avoid races accessing file

Impact: fix race

vma->vm_file reference is only stable while holding the mmap_sem,
so move usage of it to within the critical section.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 5 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4c3bd82cec49..48d1536f1ca4 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1470,13 +1470,13 @@ static inline int seq_print_user_ip(struct trace_seq *s, struct mm_struct *mm,
                         file = vma->vm_file;
                         vmstart = vma->vm_start;
                 }
+                if (file) {
+                        ret = trace_seq_path(s, &file->f_path);
+                        if (ret)
+                                ret = trace_seq_printf(s, "[+0x%lx]", ip - vmstart);
+                }
                 up_read(&mm->mmap_sem);
         }
-        if (file) {
-                ret = trace_seq_path(s, &file->f_path);
-                if (ret)
-                        ret = trace_seq_printf(s, "[+0x%lx]", ip - vmstart);
-        }
         if (ret && ((sym_flags & TRACE_ITER_SYM_ADDR) || !file))
                 ret = trace_seq_printf(s, " <" IP_FMT ">", ip);
         return ret;