Fix race condition on access to env->interrupt_request

env->interrupt_request is accessed as the bit level from both main code
and signal handler, making a race condition possible even on CISC CPU.
This causes freeze of QEMU under high load when running the dyntick
clock.

The patch below move the bit corresponding to CPU_INTERRUPT_EXIT in a
separate variable, declared as volatile sig_atomic_t, so it should be
work even on RISC CPU.

We may want to move the cpu_interrupt(env, CPU_INTERRUPT_EXIT) case in
its own function and get rid of CPU_INTERRUPT_EXIT. That can be done
later, I wanted to keep the patch short for easier review.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6728 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 6 insertions, 5 deletions

diff --git a/exec.c b/exec.c
index f4a071e0f3..902031c48d 100644
--- a/exec.c
+++ b/exec.c
@@ -1501,9 +1501,12 @@ void cpu_interrupt(CPUState *env, int mask)
 #endif
     int old_mask;
 
+    if (mask & CPU_INTERRUPT_EXIT) {
+        env->exit_request = 1;
+        mask &= ~CPU_INTERRUPT_EXIT;
+    }
+
     old_mask = env->interrupt_request;
-    /* FIXME: This is probably not threadsafe.  A different thread could
-       be in the middle of a read-modify-write operation.  */
     env->interrupt_request |= mask;
 #if defined(USE_NPTL)
     /* FIXME: TB unchaining isn't SMP safe.  For now just ignore the
@@ -1514,10 +1517,8 @@ void cpu_interrupt(CPUState *env, int mask)
     if (use_icount) {
         env->icount_decr.u16.high = 0xffff;
 #ifndef CONFIG_USER_ONLY
-        /* CPU_INTERRUPT_EXIT isn't a real interrupt.  It just means
-           an async event happened and we need to process it.  */
         if (!can_do_io(env)
-            && (mask & ~(old_mask | CPU_INTERRUPT_EXIT)) != 0) {
+            && (mask & ~old_mask) != 0) {
             cpu_abort(env, "Raised interrupt while not in I/O function");
         }
 #endif