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Reorder some operations to minimize a race condition

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This commit is contained in:
Gregory Nutt 2015-03-10 10:41:21 -06:00
parent c5c963c55d
commit 7d46801f46
2 changed files with 69 additions and 45 deletions
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8
sched/mqueue/mq_send.c
View File

@ -172,7 +172,13 @@ int mq_send(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio)
if (mqmsg)
{
/* Yes, perform the message send. */
/* Yes, perform the message send.
*
* NOTE: There is a race condition here: What if a message is added by
* interrupt related logic so that queue again becomes non-empty.
* That is handled because mq_dosend() will permit the maxmsgs limit
* to be exceeded in that case.
*/
ret = mq_dosend(mqdes, mqmsg, msg, msglen, prio);
}

106
sched/mqueue/mq_timedsend.c
View File

@ -202,8 +202,20 @@ int mq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
return ERROR;
}
/* Pre-allocate a message structure */
mqmsg = mq_msgalloc();
if (!mqmsg)
{
/* Failed to allocate the message */
set_errno(ENOMEM);
return ERROR;
}
/* Get a pointer to the message queue */
sched_lock();
msgq = mqdes->msgq;
/* OpenGroup.org: "Under no circumstance shall the operation fail with a
@ -213,16 +225,18 @@ int mq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
*
* Also ignore the time value if for some crazy reason we were called from
* an interrupt handler. This probably really should be an assertion.
*
* NOTE: There is a race condition here: What if a message is added by
* interrupt related logic so that queue again becomes non-empty. That
* is handled because mq_dosend() will permit the maxmsgs limit to be
* exceeded in that case.
*/
sched_lock();
if (msgq->nmsgs < msgq->maxmsgs || up_interrupt_context())
{
/* The message queue is not full... Ignore the time parameter and
* let mq_send do the work.
*/
/* Do the send with no further checks (possibly exceeding maxmsgs) */
ret = mq_send(mqdes, msg, msglen, prio);
ret = mq_dosend(mqdes, mqmsg, msg, msglen, prio);
sched_unlock();
return ret;
}
@ -233,9 +247,8 @@ int mq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
if (!abstime || abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
{
set_errno(EINVAL);
sched_unlock();
return ERROR;
result = EINVAL;
goto errout_with_mqmsg;
}
/* Create a watchdog. We will not actually need this watchdog
@ -246,9 +259,8 @@ int mq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
rtcb->waitdog = wd_create();
if (!rtcb->waitdog)
{
set_errno(EINVAL);
sched_unlock();
return ERROR;
result = EINVAL;
goto errout_with_mqmsg;
}
/* We are not in an interrupt handler and the message queue is full.
@ -268,33 +280,35 @@ int mq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
if (result == OK && ticks <= 0)
{
result = ETIMEDOUT;
goto errout_with_irqsave;
}
/* Handle any time-related errors */
if (result != OK)
{
set_errno(result);
ret = ERROR;
goto errout_with_irqsave;
}
/* Start the watchdog and begin the wait for MQ not full */
else
wd_start(rtcb->waitdog, ticks, (wdentry_t)mq_sndtimeout, 1, getpid());
/* And wait for the message queue to be non-empty */
ret = mq_waitsend(mqdes);
/* This may return with an error and errno set to either EINTR
* or ETIMEOUT. Cancel the watchdog timer in any event.
*/
wd_cancel(rtcb->waitdog);
/* Check if the wait failed */
if (ret < 0)
{
/* Start the watchdog */
wd_start(rtcb->waitdog, ticks, (wdentry_t)mq_sndtimeout, 1, getpid());
/* And wait for the message queue to be non-empty */
ret = mq_waitsend(mqdes);
/* This may return with an error and errno set to either EINTR
* or ETIMEOUT. Cancel the watchdog timer in any event.
*/
wd_cancel(rtcb->waitdog);
goto errout_with_irqsave;
}
/* That is the end of the atomic operations */
@ -306,26 +320,30 @@ int mq_timedsend(mqd_t mqdes, FAR const char *msg, size_t msglen, int prio,
* the message structure.
*/
if (ret == OK)
{
mqmsg = mq_msgalloc();
if (!mqmsg)
{
/* Failed to allocate the message */
set_errno(ENOMEM);
ret = ERROR;
}
else
{
/* Perform the message send. */
ret = mq_dosend(mqdes, mqmsg, msg, msglen, prio);
}
}
ret = mq_dosend(mqdes, mqmsg, msg, msglen, prio);
sched_unlock();
wd_delete(rtcb->waitdog);
rtcb->waitdog = NULL;
return ret;
/* Exit here with (1) the scheduler locked, (2) a message allocated, (3) a
* wdog allocated, and (4) interrupts disabled. The error code is in
* 'result'
*/
errout_with_irqsave:
irqrestore(saved_state);
wd_delete(rtcb->waitdog);
rtcb->waitdog = NULL;
/* Exit here with (1) the scheduler locked and 2) a message allocated. The
* error code is in 'result'
*/
errout_with_mqmsg:
mq_msgfree(mqmsg);
set_errno(result);
sched_unlock();
return ERROR;
}