tracepoint: Add signal loss events

Add signal_overflow_fail and signal_lose_info tracepoints
for signal-lost events.

Changes in v3:
 - Add docbook style comments

Changes in v2:
 - Use siginfo string macro

Suggested-by: Roland McGrath <roland@redhat.com>
Reviewed-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Oleg Nesterov <oleg@redhat.com>
LKML-Reference: <20091124215658.30449.9934.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 82 insertions, 5 deletions

diff --git a/include/trace/events/signal.h b/include/trace/events/signal.h
index a6d71de0dc0d..a510b75ac304 100644
--- a/include/trace/events/signal.h
+++ b/include/trace/events/signal.h
@@ -99,6 +99,74 @@ TRACE_EVENT(signal_deliver,
                   __entry->sig, __entry->errno, __entry->code,
                   __entry->sa_handler, __entry->sa_flags)
 );
+
+/**
+ * signal_overflow_fail - called when signal queue is overflow
+ * @sig: signal number
+ * @group: signal to process group or not (bool)
+ * @info: pointer to struct siginfo
+ *
+ * Kernel fails to generate 'sig' signal with 'info' siginfo, because
+ * siginfo queue is overflow, and the signal is dropped.
+ * 'group' is not 0 if the signal will be sent to a process group.
+ * 'sig' is always one of RT signals.
+ */
+TRACE_EVENT(signal_overflow_fail,
+
+        TP_PROTO(int sig, int group, struct siginfo *info),
+
+        TP_ARGS(sig, group, info),
+
+        TP_STRUCT__entry(
+                __field(        int,    sig     )
+                __field(        int,    group   )
+                __field(        int,    errno   )
+                __field(        int,    code    )
+        ),
+
+        TP_fast_assign(
+                __entry->sig    = sig;
+                __entry->group  = group;
+                TP_STORE_SIGINFO(__entry, info);
+        ),
+
+        TP_printk("sig=%d group=%d errno=%d code=%d",
+                  __entry->sig, __entry->group, __entry->errno, __entry->code)
+);
+
+/**
+ * signal_lose_info - called when siginfo is lost
+ * @sig: signal number
+ * @group: signal to process group or not (bool)
+ * @info: pointer to struct siginfo
+ *
+ * Kernel generates 'sig' signal but loses 'info' siginfo, because siginfo
+ * queue is overflow.
+ * 'group' is not 0 if the signal will be sent to a process group.
+ * 'sig' is always one of non-RT signals.
+ */
+TRACE_EVENT(signal_lose_info,
+
+        TP_PROTO(int sig, int group, struct siginfo *info),
+
+        TP_ARGS(sig, group, info),
+
+        TP_STRUCT__entry(
+                __field(        int,    sig     )
+                __field(        int,    group   )
+                __field(        int,    errno   )
+                __field(        int,    code    )
+        ),
+
+        TP_fast_assign(
+                __entry->sig    = sig;
+                __entry->group  = group;
+                TP_STORE_SIGINFO(__entry, info);
+        ),
+
+        TP_printk("sig=%d group=%d errno=%d code=%d",
+                  __entry->sig, __entry->group, __entry->errno, __entry->code)
+);
 #endif /* _TRACE_SIGNAL_H */
 
 /* This part must be outside protection */
diff --git a/kernel/signal.c b/kernel/signal.c
index 349d44937406..93e72e5feae6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -897,12 +897,21 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
                         break;
                 }
         } else if (!is_si_special(info)) {
-                if (sig >= SIGRTMIN && info->si_code != SI_USER)
-                /*
-                 * Queue overflow, abort.  We may abort if the signal was rt
-                 * and sent by user using something other than kill().
-                 */
+                if (sig >= SIGRTMIN && info->si_code != SI_USER) {
+                        /*
+                         * Queue overflow, abort.  We may abort if the
+                         * signal was rt and sent by user using something
+                         * other than kill().
+                         */
+                        trace_signal_overflow_fail(sig, group, info);
                         return -EAGAIN;
+                } else {
+                        /*
+                         * This is a silent loss of information.  We still
+                         * send the signal, but the *info bits are lost.
+                         */
+                        trace_signal_lose_info(sig, group, info);
+                }
         }
 
 out_set: