From bb8da4303851642318b626aad507ab7c39f6a80d Mon Sep 17 00:00:00 2001
From: Alexey Tikhonov <atikhono@redhat.com>
Date: Mon, 1 Nov 2021 20:09:02 +0100
Subject: [PATCH] DEBUG: avoid backtrace dups.
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In case the same error(s) is repeated again and again repeating the same
backtrace doesn't add much value. In this case let's add just a note.

Reviewed-by: Tomáš Halman <thalman@redhat.com>
---
 src/util/debug.c           |  4 +--
 src/util/debug_backtrace.c | 51 +++++++++++++++++++++++++++++++++++---
 2 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/src/util/debug.c b/src/util/debug.c
index 7c03fb7df..953123718 100644
--- a/src/util/debug.c
+++ b/src/util/debug.c
@@ -42,7 +42,7 @@
 void sss_debug_backtrace_init(void);
 void sss_debug_backtrace_vprintf(int level, const char *format, va_list ap);
 void sss_debug_backtrace_printf(int level, const char *format, ...);
-void sss_debug_backtrace_endmsg(int level);
+void sss_debug_backtrace_endmsg(const char *file, long line, int level);
 
 const char *debug_prg_name = "sssd";
 
@@ -359,7 +359,7 @@ void sss_vdebug_fn(const char *file,
     if (flags & APPEND_LINE_FEED) {
         sss_debug_backtrace_printf(level, "\n");
     }
-    sss_debug_backtrace_endmsg(level);
+    sss_debug_backtrace_endmsg(file, line, level);
 }
 
 void sss_debug_fn(const char *file,
diff --git a/src/util/debug_backtrace.c b/src/util/debug_backtrace.c
index d99325ab6..e376f815b 100644
--- a/src/util/debug_backtrace.c
+++ b/src/util/debug_backtrace.c
@@ -30,6 +30,9 @@ extern FILE *_sss_debug_file;
 static const unsigned SSS_DEBUG_BACKTRACE_DEFAULT_SIZE = 100*1024; /* bytes */
 static const unsigned SSS_DEBUG_BACKTRACE_LEVEL        = SSSDBG_BE_FO;
 
+/* Size of locations history to keep to avoid duplicating backtraces */
+#define SSS_DEBUG_BACKTRACE_LOCATIONS 5
+
 
 /*                     -->
  * ring buffer = [*******t...\n............e000]
@@ -46,12 +49,21 @@ static struct {
     char     *buffer;  /* buffer start */
     char     *end;     /* end data border */
     char     *tail;    /* tail of "current" message */
+
+    /* locations where last backtraces happened */
+    struct {
+        const char *file;
+        long        line;
+    } locations[SSS_DEBUG_BACKTRACE_LOCATIONS];
+    unsigned last_location_idx;
 } _bt;
 
 
 static inline bool _all_levels_enabled(void);
 static inline bool _backtrace_is_enabled(int level);
 static inline bool _is_trigger_level(int level);
+static void _store_location(const char *file, long line);
+static bool _is_recent_location(const char *file, long line);
 static void _backtrace_vprintf(const char *format, va_list ap);
 static void _backtrace_printf(const char *format, ...);
 static void _backtrace_dump(void);
@@ -75,6 +87,8 @@ void sss_debug_backtrace_init(void)
     _bt.enabled     = true;
     _bt.initialized = true;
 
+    /* locations[] & last_location_idx are zero-initialized */
+
     _backtrace_printf("   *  ");
 }
 
@@ -116,7 +130,7 @@ void sss_debug_backtrace_printf(int level, const char *format, ...)
 }
 
 
-void sss_debug_backtrace_endmsg(int level)
+void sss_debug_backtrace_endmsg(const char *file, long line, int level)
 {
     if (DEBUG_IS_SET(level)) {
         _debug_fflush();
@@ -124,7 +138,16 @@ void sss_debug_backtrace_endmsg(int level)
 
     if (_backtrace_is_enabled(level)) {
         if (_is_trigger_level(level)) {
-            _backtrace_dump();
+            if (!_is_recent_location(file, line)) {
+                _backtrace_dump();
+                _store_location(file, line);
+            } else {
+                fprintf(_sss_debug_file ? _sss_debug_file : stderr,
+                        "   *  ... skipping repetitive backtrace ...\n");
+                /* and reset */
+                _bt.end  = _bt.buffer;
+                _bt.tail = _bt.buffer;
+            }
         }
         _backtrace_printf("   *  ");
     }
@@ -191,7 +214,29 @@ static inline bool _backtrace_is_enabled(int level)
 }
 
 
- /* prints to buffer */
+static void _store_location(const char *file, long line)
+{
+    _bt.last_location_idx = (_bt.last_location_idx + 1) % SSS_DEBUG_BACKTRACE_LOCATIONS;
+     /* __FILE__ is a character string literal with static storage duration. */
+    _bt.locations[_bt.last_location_idx].file = file;
+    _bt.locations[_bt.last_location_idx].line = line;
+}
+
+
+static bool _is_recent_location(const char *file, long line)
+{
+    for (unsigned idx = 0; idx < SSS_DEBUG_BACKTRACE_LOCATIONS; ++idx) {
+        if ((line == _bt.locations[idx].line) &&
+            (_bt.locations[idx].file != NULL) &&
+            (strcmp(file, _bt.locations[idx].file) == 0)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+
+/* prints to buffer */
 static void _backtrace_vprintf(const char *format, va_list ap)
 {
     int buff_tail_size = _bt.size - (_bt.tail - _bt.buffer);
-- 
2.26.3