Re: [Xenomai-core] xenomai-solo vxWorks: know whether a task is safe or not

[Philippe Gerum]

Niklaus Giger wrote:
> Hi
> 
> For various reasons we were forced to examine under vxWorks 5.5 the private
> WIND_TCB safeCnt field to determine whether a task was "safe" or not.
> 
> With the attached patch I try to add a taskIsSafe procedure to xenomai-solo.
> It is probably not free from race condition, as I do not know how to access
> a pthread_mutex.
> 
> Would such (may be improved) patch find its way into the "official" trunk?
> 

Assuming that VxWorks tracks the locking depth in safeCnt, that implementation
would not properly account for nested locking (safelock is a recursive mutex).
Additionally, since WIND_TCB is something of a semi-public structure in 5.x and
earlier versions, we could just track the safe counter there as well, instead of
adding a non-standard taskIsSafe() call; we already do that for the status field
anyway. Here is a possible implementation:

diff --git a/include/vxworks/taskLib.h b/include/vxworks/taskLib.h
index 510dabb..6334396 100644
--- a/include/vxworks/taskLib.h
+++ b/include/vxworks/taskLib.h
@@ -49,6 +49,7 @@ typedef struct WIND_TCB {
        void *opaque;
        int magic;
        int status;
+       int safeCnt;
        int flags;
        FUNCPTR entry;
 } WIND_TCB;
diff --git a/vxworks/taskLib.c b/vxworks/taskLib.c
index f6253b2..a9e12e7 100644
--- a/vxworks/taskLib.c
+++ b/vxworks/taskLib.c
@@ -283,7 +283,6 @@ static STATUS __taskInit(struct wind_task *task,
        int ret;

        ret = check_task_priority(prio);
-
        if (ret) {
                errno = ret;
                return ERROR;
@@ -307,6 +306,7 @@ static STATUS __taskInit(struct wind_task *task,
        tcb->magic = task_magic;
        tcb->opaque = task;
        tcb->status = WIND_SUSPEND;
+       tcb->safeCnt = 0;
        tcb->flags = flags;
        tcb->entry = entry;

@@ -588,13 +588,13 @@ STATUS taskSafe(void)
        }

        current = wind_task_current();
-
        if (current == NULL) {
                errno = S_objLib_OBJ_NO_METHOD;
                return ERROR;
        }

        pthread_mutex_lock(&current->safelock);
+       current->tcb->safeCnt++;

        return OK;
 }
@@ -602,6 +602,7 @@ STATUS taskSafe(void)
 STATUS taskUnsafe(void)
 {
        struct wind_task *current;
+       int ret;

        if (threadobj_async_p()) {
                errno = S_intLib_NOT_ISR_CALLABLE;
@@ -609,13 +610,14 @@ STATUS taskUnsafe(void)
        }

        current = wind_task_current();
-
        if (current == NULL) {
                errno = S_objLib_OBJ_NO_METHOD;
                return ERROR;
        }

-       pthread_mutex_unlock(&current->safelock);
+       ret = pthread_mutex_unlock(&current->safelock);
+       if (ret == 0)
+               current->tcb->safeCnt--;

        return OK;
 }

-- 
Philippe.


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