lib: tevent: make TEVENT_SIG_INCREMENT atomic.

On arm platforms incrementing a variable is not
an atomic operation, so may be interrupted by
signal processing (if a signal interrupts another
signal handler).

Use compiler built-ins to make this atomic.
__sync_fetch_and_add() works on gcc, llvm,
IBM xlC on AIX, and Intel icc (10.1 and
above).

atomic_add_32() works on Oracle Solaris.

Based on an inital patch from kamei@osstech.co.jp.

Bug #10640 - smbd is not responding - tevent_common_signal_handler() increments non-atomic variables

https://bugzilla.samba.org/show_bug.cgi?id=10640

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <Volker.Lendecke@SerNet.DE>

diff --git a/lib/replace/replace.h b/lib/replace/replace.h
index f940898e4b9b796781e889b6e85c085edea67091..bc40bf012e68d68b351ab7a7f4f98d11b9f07959 100644 (file)
--- a/lib/replace/replace.h
+++ b/lib/replace/replace.h
@@ -904,4 +904,9 @@ bool nss_wrapper_hosts_enabled(void);
 bool socket_wrapper_enabled(void);
 bool uid_wrapper_enabled(void);
 
+/* Needed for Solaris atomic_add_XX functions. */
+#if defined(HAVE_SYS_ATOMIC_H)
+#include <sys/atomic.h>
+#endif
+
 #endif /* _LIBREPLACE_REPLACE_H */

diff --git a/lib/replace/wscript b/lib/replace/wscript
index a26de0f8bae7f401b9804c8a56c83f86f050ac3c..22dd1322a210ecd1913d3ad68dc622ac36f6de6e 100644 (file)
--- a/lib/replace/wscript
+++ b/lib/replace/wscript
@@ -110,6 +110,7 @@ struct foo bar = { .y = 'X', .x = 1 };
     conf.CHECK_HEADERS('sys/extattr.h sys/ea.h sys/proplist.h sys/cdefs.h')
     conf.CHECK_HEADERS('utmp.h utmpx.h lastlog.h malloc.h')
     conf.CHECK_HEADERS('syscall.h sys/syscall.h inttypes.h')
+    conf.CHECK_HEADERS('sys/atomic.h')
 
     # Check for process set name support
     conf.CHECK_CODE('''
@@ -229,6 +230,30 @@ struct foo bar = { .y = 'X', .x = 1 };
                        msg="Checking whether we have ucontext_t",
                        headers='signal.h sys/ucontext.h')
 
+    # Check for atomic builtins. */
+    conf.CHECK_CODE('''
+                    int main(void) {
+                        int i;
+                        (void)__sync_fetch_and_add(&i, 1);
+                        return 0;
+                    }
+                    ''',
+                    'HAVE___SYNC_FETCH_AND_ADD',
+                    msg='Checking for __sync_fetch_and_add compiler builtin')
+
+    conf.CHECK_CODE('''
+                    #include <stdint.h>
+                    #include <sys/atomic.h>
+                    int main(void) {
+                        int32_t i;
+                        atomic_add_32(&i, 1);
+                        return 0;
+                    }
+                    ''',
+                    'HAVE_ATOMIC_ADD_32',
+                    headers='stdint.h sys/atomic.h',
+                    msg='Checking for atomic_add_32 compiler builtin')
+
     # these may be builtins, so we need the link=False strategy
     conf.CHECK_FUNCS('strdup memmem printf memset memcpy memmove strcpy strncpy bzero', link=False)
 

diff --git a/lib/tevent/tevent_signal.c b/lib/tevent/tevent_signal.c
index 1ff487256e937e7f9c9f83b9f941a619b04dcff0..b54da2ede82b55426159f0fb8e020e55b098eb52 100644 (file)
--- a/lib/tevent/tevent_signal.c
+++ b/lib/tevent/tevent_signal.c
@@ -52,7 +52,13 @@ struct tevent_sigcounter {
        uint32_t seen;
 };
 
+#if defined(HAVE___SYNC_FETCH_AND_ADD)
+#define TEVENT_SIG_INCREMENT(s) __sync_fetch_and_add(&((s).count), 1)
+#elif defined(HAVE_ATOMIC_ADD_32)
+#define TEVENT_SIG_INCREMENT(s) atomic_add_32(&((s).count), 1)
+#else
 #define TEVENT_SIG_INCREMENT(s) (s).count++
+#endif
 #define TEVENT_SIG_SEEN(s, n) (s).seen += (n)
 #define TEVENT_SIG_PENDING(s) ((s).seen != (s).count)