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-rw-r--r--arch/um/include/sysdep-i386/barrier.h9
-rw-r--r--arch/um/include/sysdep-x86_64/barrier.h7
-rw-r--r--arch/um/os-Linux/signal.c31
3 files changed, 44 insertions, 3 deletions
diff --git a/arch/um/include/sysdep-i386/barrier.h b/arch/um/include/sysdep-i386/barrier.h
new file mode 100644
index 00000000000..b58d52c5b2f
--- /dev/null
+++ b/arch/um/include/sysdep-i386/barrier.h
@@ -0,0 +1,9 @@
+#ifndef __SYSDEP_I386_BARRIER_H
+#define __SYSDEP_I386_BARRIER_H
+
+/* Copied from include/asm-i386 for use by userspace. i386 has the option
+ * of using mfence, but I'm just using this, which works everywhere, for now.
+ */
+#define mb() asm volatile("lock; addl $0,0(%esp)")
+
+#endif
diff --git a/arch/um/include/sysdep-x86_64/barrier.h b/arch/um/include/sysdep-x86_64/barrier.h
new file mode 100644
index 00000000000..7b610befdc8
--- /dev/null
+++ b/arch/um/include/sysdep-x86_64/barrier.h
@@ -0,0 +1,7 @@
+#ifndef __SYSDEP_X86_64_BARRIER_H
+#define __SYSDEP_X86_64_BARRIER_H
+
+/* Copied from include/asm-x86_64 for use by userspace. */
+#define mb() asm volatile("mfence":::"memory")
+
+#endif
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 6b81739279d..b897e8592d7 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -15,6 +15,7 @@
#include "user.h"
#include "signal_kern.h"
#include "sysdep/sigcontext.h"
+#include "sysdep/barrier.h"
#include "sigcontext.h"
#include "mode.h"
#include "os.h"
@@ -34,8 +35,12 @@
#define SIGALRM_BIT 2
#define SIGALRM_MASK (1 << SIGALRM_BIT)
-static int signals_enabled = 1;
-static int pending = 0;
+/* These are used by both the signal handlers and
+ * block/unblock_signals. I don't want modifications cached in a
+ * register - they must go straight to memory.
+ */
+static volatile int signals_enabled = 1;
+static volatile int pending = 0;
void sig_handler(int sig, struct sigcontext *sc)
{
@@ -152,6 +157,12 @@ int change_sig(int signal, int on)
void block_signals(void)
{
signals_enabled = 0;
+ /* This must return with signals disabled, so this barrier
+ * ensures that writes are flushed out before the return.
+ * This might matter if gcc figures out how to inline this and
+ * decides to shuffle this code into the caller.
+ */
+ mb();
}
void unblock_signals(void)
@@ -171,9 +182,23 @@ void unblock_signals(void)
*/
signals_enabled = 1;
+ /* Setting signals_enabled and reading pending must
+ * happen in this order.
+ */
+ mb();
+
save_pending = pending;
- if(save_pending == 0)
+ if(save_pending == 0){
+ /* This must return with signals enabled, so
+ * this barrier ensures that writes are
+ * flushed out before the return. This might
+ * matter if gcc figures out how to inline
+ * this (unlikely, given its size) and decides
+ * to shuffle this code into the caller.
+ */
+ mb();
return;
+ }
pending = 0;