Module: xenomai-rpm
Branch: for-upstream
Commit: ac5c739dabcb14334c2e390a9e3064f11f97283c
URL:
http://git.xenomai.org/?p=xenomai-rpm.git;a=commit;h=ac5c739dabcb14334c2e390a9e3064f11f97283c
Author: Philippe Gerum <r...@xenomai.org>
Date: Sat May 1 18:22:40 2010 +0200
nucleus/shadow: revert commit 96f5fa2
This patch reverts 96f5fa2, which did fix a real bug, but the wrong
way. It broke basic assumptions in RPI management wrt SMP,
introducing races in rpi_clear_remote() and xnshadow_rpi_check() at
least, regarding the update of the RPI backlink (i.e. thread->rpi).
Those assumptions are as follows:
- RPI queues are per-CPU, and threads may enter/leave them only from
the CPU they belong to, with one exception: rpi_clear_remote().
- threads may enter/leave RPI queues when they are in a state mutually
exclusive to running rpi_clear_remote().
---
ksrc/nucleus/shadow.c | 70 ++++++++++++++++++++++--------------------------
1 files changed, 32 insertions(+), 38 deletions(-)
diff --git a/ksrc/nucleus/shadow.c b/ksrc/nucleus/shadow.c
index 872c37f..873a9bc 100644
--- a/ksrc/nucleus/shadow.c
+++ b/ksrc/nucleus/shadow.c
@@ -170,40 +170,6 @@ static inline void set_switch_lock_owner(struct
task_struct *p)
#define rpi_p(t) ((t)->rpi != NULL)
-static struct xnthread *rpi_next(struct xnsched *sched, spl_t s)
-{
- struct xnthread *thread;
-
- thread = xnsched_peek_rpi(sched);
- while (thread &&
- xnthread_user_task(thread)->state != TASK_RUNNING &&
- !xnthread_test_info(thread, XNATOMIC)) {
- /*
- * A blocked Linux task must be removed from the RPI
- * list. Checking for XNATOMIC prevents from unlinking
- * a thread which is currently in flight to the
- * primary domain (see xnshadow_harden()); not doing
- * so would open a tiny window for priority inversion.
- *
- * BIG FAT WARNING: Do not consider a blocked thread
- * linked to another processor's RPI list for removal,
- * since this may happen if such thread immediately
- * resumes on the remote CPU.
- */
- xnsched_pop_rpi(thread);
- thread->rpi = NULL;
- xnlock_put_irqrestore(&sched->rpilock, s);
- /* Do NOT nest the rpilock and nklock locks. */
- xnlock_get_irqsave(&nklock, s);
- xnsched_suspend_rpi(thread);
- xnlock_put_irqrestore(&nklock, s);
- xnlock_get_irqsave(&sched->rpilock, s);
- thread = xnsched_peek_rpi(sched);
- }
-
- return thread;
-}
-
static void rpi_push(struct xnsched *sched, struct xnthread *thread)
{
struct xnsched_class *sched_class;
@@ -266,7 +232,7 @@ static void rpi_pop(struct xnthread *thread)
return;
}
- top = rpi_next(sched, s);
+ top = xnsched_peek_rpi(sched);
if (likely(top == NULL)) {
prio = XNSCHED_IDLE_PRIO;
sched_class = &xnsched_class_idle;
@@ -340,7 +306,7 @@ static void rpi_clear_remote(struct xnthread *thread)
xnsched_pop_rpi(thread);
thread->rpi = NULL;
- if (rpi_next(rpi, s) == NULL)
+ if (xnsched_peek_rpi(rpi) == NULL)
rcpu = xnsched_cpu(rpi);
xnlock_put_irqrestore(&rpi->rpilock, s);
@@ -404,12 +370,40 @@ static inline void rpi_switch(struct task_struct
*next_task)
oldprio = xnsched_root_priority(sched);
oldclass = xnsched_root_class(sched);
+ if (prev &&
+ current->state != TASK_RUNNING &&
+ !xnthread_test_info(prev, XNATOMIC)) {
+ /*
+ * A blocked Linux task must be removed from the RPI
+ * list. Checking for XNATOMIC prevents from unlinking
+ * a thread which is currently in flight to the
+ * primary domain (see xnshadow_harden()); not doing
+ * so would open a tiny window for priority inversion.
+ *
+ * BIG FAT WARNING: Do not consider a blocked thread
+ * linked to another processor's RPI list for removal,
+ * since this may happen if such thread immediately
+ * resumes on the remote CPU.
+ */
+ xnlock_get_irqsave(&sched->rpilock, s);
+ if (prev->rpi == sched) {
+ xnsched_pop_rpi(prev);
+ prev->rpi = NULL;
+ xnlock_put_irqrestore(&sched->rpilock, s);
+ /* Do NOT nest the rpilock and nklock locks. */
+ xnlock_get_irqsave(&nklock, s);
+ xnsched_suspend_rpi(prev);
+ xnlock_put_irqrestore(&nklock, s);
+ } else
+ xnlock_put_irqrestore(&sched->rpilock, s);
+ }
+
if (next == NULL ||
next_task->policy != SCHED_FIFO ||
xnthread_test_state(next, XNRPIOFF)) {
xnlock_get_irqsave(&sched->rpilock, s);
- top = rpi_next(sched, s);
+ top = xnsched_peek_rpi(sched);
if (top) {
newprio = top->cprio;
newclass = top->sched_class;
@@ -498,7 +492,7 @@ void xnshadow_rpi_check(void)
spl_t s;
xnlock_get_irqsave(&sched->rpilock, s);
- top = rpi_next(sched, s);
+ top = xnsched_peek_rpi(sched);
xnlock_put_irqrestore(&sched->rpilock, s);
if (top == NULL && xnsched_root_class(sched) != &xnsched_class_idle)
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