On 09/11/2011 04:29 PM, Jan Kiszka wrote:
> On 2011-09-11 16:24, Gilles Chanteperdrix wrote:
>> On 09/11/2011 12:50 PM, Jan Kiszka wrote:
>>> Hi all,
>>>
>>> just looked into the hrescnt issue again, specifically the corner case
>>> of a shadow thread switching from real-time policy to SCHED_OTHER.
>>
>> Doing this while holding a mutex looks invalid.
>
> Looking at POSIX e.g., is there anything in the spec that makes this
> invalid? If the kernel preserves or established proper priority
> boosting, I do not see what could break in principle.
>
> It is nothing I would design into some app, but we should somehow handle
> it (doc update or code adjustments).
>
>> If we do not do it, the current code is valid.
>
> Except for its dependency on XNOTHER which is not updated on RT->NORMAL
> transitions.
The fact that this update did not take place made the code work. No
negative rescnt could happen with that code.
Anyway, here is a patch to allow switching back from RT to NORMAL, but
send a SIGDEBUG to a thread attempting to release a mutex while its
counter is already 0. We end up avoiding a big chunk of code that would
have been useful for a really strange corner case.
diff --git a/examples/native/sigdebug.c b/examples/native/sigdebug.c
index e20714b..7b840f9 100644
--- a/examples/native/sigdebug.c
+++ b/examples/native/sigdebug.c
@@ -34,6 +34,8 @@ static const char *reason_str[] = {
[SIGDEBUG_MIGRATE_PRIOINV] = "affected by priority inversion",
[SIGDEBUG_NOMLOCK] = "missing mlockall",
[SIGDEBUG_WATCHDOG] = "runaway thread",
+ [SIGDEBUG_SCHED_CHANGE_W_MX] =
+ "switched to SCHED_OTHER policy with mutex held",
};
void warn_upon_switch(int sig, siginfo_t *si, void *context)
diff --git a/include/asm-generic/syscall.h b/include/asm-generic/syscall.h
index a9cdc87..5b6c764 100644
--- a/include/asm-generic/syscall.h
+++ b/include/asm-generic/syscall.h
@@ -61,6 +61,7 @@ typedef struct xnsysinfo {
#define SIGDEBUG_MIGRATE_PRIOINV 4
#define SIGDEBUG_NOMLOCK 5
#define SIGDEBUG_WATCHDOG 6
+#define SIGDEBUG_SCHED_CHANGE_W_MX 7
#ifdef __KERNEL__
diff --git a/include/nucleus/sched-idle.h b/include/nucleus/sched-idle.h
index 6399a17..3cc7185 100644
--- a/include/nucleus/sched-idle.h
+++ b/include/nucleus/sched-idle.h
@@ -39,6 +39,7 @@ extern struct xnsched_class xnsched_class_idle;
static inline void __xnsched_idle_setparam(struct xnthread *thread,
const union xnsched_policy_param *p)
{
+ xnthread_set_state(thread, XNOTHER);
thread->cprio = p->idle.prio;
}
diff --git a/include/nucleus/sched-rt.h b/include/nucleus/sched-rt.h
index 71f655c..d17b058 100644
--- a/include/nucleus/sched-rt.h
+++ b/include/nucleus/sched-rt.h
@@ -86,6 +86,10 @@ static inline void __xnsched_rt_setparam(struct xnthread
*thread,
const union xnsched_policy_param *p)
{
thread->cprio = p->rt.prio;
+ if (thread->cprio)
+ xnthread_clear_state(thread, XNOTHER);
+ else
+ xnthread_set_state(thread, XNOTHER);
}
static inline void __xnsched_rt_getparam(struct xnthread *thread,
diff --git a/ksrc/nucleus/pod.c b/ksrc/nucleus/pod.c
index 9a02e80..d19999f 100644
--- a/ksrc/nucleus/pod.c
+++ b/ksrc/nucleus/pod.c
@@ -1896,16 +1896,6 @@ int __xnpod_set_thread_schedparam(struct xnthread
*thread,
xnsched_putback(thread);
#ifdef CONFIG_XENO_OPT_PERVASIVE
- /*
- * A non-real-time shadow may upgrade to real-time FIFO
- * scheduling, but the latter may never downgrade to
- * SCHED_NORMAL Xenomai-wise. In the valid case, we clear
- * XNOTHER to reflect the change. Note that we keep handling
- * non real-time shadow specifics in higher code layers, not
- * to pollute the core scheduler with peculiarities.
- */
- if (sched_class == &xnsched_class_rt && sched_param->rt.prio > 0)
- xnthread_clear_state(thread, XNOTHER);
if (propagate) {
if (xnthread_test_state(thread, XNRELAX))
xnshadow_renice(thread);
diff --git a/ksrc/nucleus/sched-sporadic.c b/ksrc/nucleus/sched-sporadic.c
index fd37c21..587be4a 100644
--- a/ksrc/nucleus/sched-sporadic.c
+++ b/ksrc/nucleus/sched-sporadic.c
@@ -258,6 +258,7 @@ static void xnsched_sporadic_setparam(struct xnthread
*thread,
}
}
+ xnthread_clear_state(thread, XNOTHER);
thread->cprio = p->pss.current_prio;
}
diff --git a/ksrc/nucleus/sched-tp.c b/ksrc/nucleus/sched-tp.c
index 43a548e..2423e81 100644
--- a/ksrc/nucleus/sched-tp.c
+++ b/ksrc/nucleus/sched-tp.c
@@ -100,6 +100,7 @@ static void xnsched_tp_setparam(struct xnthread *thread,
{
struct xnsched *sched = thread->sched;
+ xnthread_clear_state(thread, XNOTHER);
thread->tps = &sched->tp.partitions[p->tp.ptid];
thread->cprio = p->tp.prio;
}
diff --git a/ksrc/nucleus/synch.c b/ksrc/nucleus/synch.c
index b956e46..e3442a4 100644
--- a/ksrc/nucleus/synch.c
+++ b/ksrc/nucleus/synch.c
@@ -684,9 +684,13 @@ xnsynch_release_thread(struct xnsynch *synch, struct
xnthread *lastowner)
XENO_BUGON(NUCLEUS, !testbits(synch->status, XNSYNCH_OWNER));
- if (xnthread_test_state(lastowner, XNOTHER))
- xnthread_dec_rescnt(lastowner);
- XENO_BUGON(NUCLEUS, xnthread_get_rescnt(lastowner) < 0);
+ if (xnthread_test_state(lastowner, XNOTHER)) {
+ if (xnthread_get_rescnt(lastowner))
+ xnshadow_send_sig(lastowner, SIGDEBUG,
+ SIGDEBUG_SCHED_CHANGE_W_MX, 1);
+ else
+ xnthread_dec_rescnt(lastowner);
+ }
lastownerh = xnthread_handle(lastowner);
if (use_fastlock &&
--
Gilles.
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