[S] Change in libosmocore[master]: logging: Avoid infinite loop logging inside logging path

[pespin]

pespin has uploaded this change for review. ( 
https://gerrit.osmocom.org/c/libosmocore/+/41978?usp=email )


Change subject: logging: Avoid infinite loop logging inside logging path
......................................................................

logging: Avoid infinite loop logging inside logging path

If eg. gsmtap_log target is requested to log a message but the iofd
wqueue is full, it may try to log an error message, which will create an
infinite stack loop.

Change-Id: If3b8c0ee97537242162558fdd1c99f03b32af811
---
M include/osmocom/core/logging_internal.h
M src/core/logging.c
2 files changed, 22 insertions(+), 4 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/78/41978/1

diff --git a/include/osmocom/core/logging_internal.h 
b/include/osmocom/core/logging_internal.h
index 68d4c4b..0cc82a4 100644
--- a/include/osmocom/core/logging_internal.h
+++ b/include/osmocom/core/logging_internal.h
@@ -4,16 +4,25 @@
  *  @{
  * \file logging_internal.h */

+#include <stdbool.h>
 #include <osmocom/core/logging.h>
 #include <osmocom/core/utils.h>

 /* maximum length of the log string of a single log event (typically  line) */
 #define MAX_LOG_SIZE   4096

+struct log_thread_state {
+       /* Whether we are inside a code path to generate logging output: */
+       bool logging_active;
+       /* Cache TID: */
+       long int tid;
+};
+
 extern void *tall_log_ctx;
 extern struct log_info *osmo_log_info;
 extern const struct value_string loglevel_strs[];
 extern struct llist_head osmo_log_target_list;
+extern __thread struct log_thread_state log_thread_state;

 void assert_loginfo(const char *src);

diff --git a/src/core/logging.c b/src/core/logging.c
index af5698a..72c24bb 100644
--- a/src/core/logging.c
+++ b/src/core/logging.c
@@ -84,7 +84,7 @@
 void *tall_log_ctx = NULL;
 LLIST_HEAD(osmo_log_target_list);

-static __thread long int logging_tid;
+__thread struct log_thread_state log_thread_state;

 #if (!EMBEDDED)
 /*! One global copy that contains the union of log levels for all targets
@@ -606,9 +606,9 @@
                        OSMO_STRBUF_PRINTF(sb, " ");
                }
                if (target->print_tid) {
-                       if (logging_tid == 0)
-                               logging_tid = (long int)osmo_gettid();
-                       OSMO_STRBUF_PRINTF(sb, "%ld ", logging_tid);
+                       if (log_thread_state.tid == 0)
+                               log_thread_state.tid = (long int)osmo_gettid();
+                       OSMO_STRBUF_PRINTF(sb, "%ld ", log_thread_state.tid);
                }
                if (target->print_category)
                        OSMO_STRBUF_PRINTF(sb, "%s%s%s%s ",
@@ -743,6 +743,14 @@
 {
        struct log_target *tar;

+       if (OSMO_UNLIKELY(log_thread_state.logging_active)) {
+               /* Avoid re-entrant logging: If logging to log target generates
+               * extra logging (eg. an error log line duet o some wqueue being 
full),
+               * we may end up in an infinite loop. */
+               return;
+       }
+       log_thread_state.logging_active = true;
+
        subsys = map_subsys(subsys);

 #if !defined(EMBEDDED)
@@ -776,6 +784,7 @@
        }

        log_tgt_mutex_unlock();
+       log_thread_state.logging_active = false;
 }

 /*! logging function used by DEBUGP() macro

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Gerrit-MessageType: newchange
Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: If3b8c0ee97537242162558fdd1c99f03b32af811
Gerrit-Change-Number: 41978
Gerrit-PatchSet: 1
Gerrit-Owner: pespin <pes...@sysmocom.de>