[Qemu-devel] [PATCH 2/8] exec: don't use cpu_index to detect if cpu_exec_init()'s been called for cpu

[Igor Mammedov <imammedo@redhat.com>]

Instead use QTAIL's tqe_prev field to detect if cpu's been
placed in list by cpu_exec_init() which is always set if
QTAIL element is in list.

Fixes SIGSEGV on failure path in case cpu_index is assigned
by board and cpu.relalize() fails before cpu_exec_init() is called.

In follow up patches, cpu_index will be assigned by boards that
support cpu hot(un)plug and need stable cpu_index that doesn't
depend on order cpus are created/removed.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reported-by: David Gibson <david@gibson.dropbear.id.au>
---
 include/qemu/queue.h | 2 ++
 exec.c               | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/qemu/queue.h b/include/qemu/queue.h
index c2b6c81..2c2c74b 100644
--- a/include/qemu/queue.h
+++ b/include/qemu/queue.h
@@ -407,6 +407,7 @@ struct {                                                                \
         else                                                            \
                 (head)->tqh_last = (elm)->field.tqe_prev;               \
         *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
+        (elm)->field.tqe_prev = NULL;                                   \
 } while (/*CONSTCOND*/0)
 
 #define QTAILQ_FOREACH(var, head, field)                                \
@@ -430,6 +431,7 @@ struct {                                                                \
 #define QTAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
 #define QTAILQ_FIRST(head)               ((head)->tqh_first)
 #define QTAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
+#define QTAILQ_IN_USE(elm, field)        ((elm)->field.tqe_prev)
 
 #define QTAILQ_LAST(head, headname) \
         (*(((struct headname *)((head)->tqh_last))->tqh_last))
diff --git a/exec.c b/exec.c
index 2f57c62..8c5da32 100644
--- a/exec.c
+++ b/exec.c
@@ -643,8 +643,8 @@ void cpu_exec_exit(CPUState *cpu)
     CPUClass *cc = CPU_GET_CLASS(cpu);
 
     cpu_list_lock();
-    if (cpu->cpu_index == -1) {
-        /* cpu_index was never allocated by this @cpu or was already freed. */
+    if (!QTAILQ_IN_USE(cpu, node)) {
+        /* there is nothing to undo since cpu_exec_init() hasn't been called */
         cpu_list_unlock();
         return;
     }
-- 
2.7.4