tracing: Don't use p->len field to determine output in __print_*() functions

If more than one __print_*() function is used in a tracepoint
(__print_flags(), __print_symbols(), etc), then the temp seq buffer will
not be zero on entry. Using the temp seq buffer's length to know if
data has been printed or not in the current function is incorrect and
may produce incorrect results.

Currently, no in-tree tracepoint causes this bug, but new ones may
be created.

Cc: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 3efd718984fbbbc00b0a2aef23c408fce271b924..c5a01873567d45b04f6b6ddcbef5a29aad8d1103 100644 (file)
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -319,7 +319,7 @@ ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
 
        /* check for left over flags */
        if (flags) {
-               if (p->len && delim)
+               if (!first && delim)
                        trace_seq_puts(p, delim);
                trace_seq_printf(p, "0x%lx", flags);
        }
@@ -346,7 +346,7 @@ ftrace_print_symbols_seq(struct trace_seq *p, unsigned long val,
                break;
        }
 
-       if (!p->len)
+       if (ret == (const char *)(p->buffer + p->len))
                trace_seq_printf(p, "0x%lx", val);
                
        trace_seq_putc(p, 0);
@@ -372,7 +372,7 @@ ftrace_print_symbols_seq_u64(struct trace_seq *p, unsigned long long val,
                break;
        }
 
-       if (!p->len)
+       if (ret == (const char *)(p->buffer + p->len))
                trace_seq_printf(p, "0x%llx", val);
 
        trace_seq_putc(p, 0);