[Qemu-devel] Re: [PATCH] fix smp with tcg mode and --enable-io-thread

[Jan Kiszka]

Jan Kiszka wrote:
> And there is some race that cause a lock up in qemu_mutex_lock_iothread
> after a while (the cpu_unlink_tb seems to race with the linking - just a
> guess so far).

This seems to fix a long-standing race between cpu_exec and
signal-driven cpu_unlink_tb:

diff --git a/cpu-exec.c b/cpu-exec.c
index 026980a..bfc34e4 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -599,8 +598,9 @@ int cpu_exec(CPUState *env1)
                    TB, but before it is linked into a potentially
                    infinite loop and becomes env->current_tb. Avoid
                    starting execution if there is a pending interrupt. */
-                if (!unlikely (env->exit_request)) {
-                    env->current_tb = tb;
+                env->current_tb = tb;
+                asm("");
+                if (likely(!env->exit_request)) {
                     tc_ptr = tb->tc_ptr;
                 /* execute the generated code */
 #if defined(__sparc__) && !defined(CONFIG_SOLARIS)
@@ -609,7 +609,6 @@ int cpu_exec(CPUState *env1)
 #define env cpu_single_env
 #endif
                     next_tb = tcg_qemu_tb_exec(tc_ptr);
-                    env->current_tb = NULL;
                     if ((next_tb & 3) == 2) {
                         /* Instruction counter expired.  */
                         int insns_left;
@@ -638,6 +637,7 @@ int cpu_exec(CPUState *env1)
                         }
                     }
                 }
+                env->current_tb = NULL;
                 /* reset soft MMU for next block (it can currently
                    only be set by a memory fault) */
             } /* for(;;) */

Still testing, though.

Jan

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