Hi, I tried my best to understand the logic behind unlock and
merge_pending routines and come up with this fix that works for me.
I split the lockcount handling in 2 parts when lockcount is > 1 just
decrement fast as always,
but when it's 1 we enter critical section and make it 0 inside
it(pre-emption is enabled).
I think there is a small time after decrement in the if statement and
enter_critical_section_wo_note() in original code where can race happen.
Does this make sense? Sorry if it's a dumb question - scheduler stuff
with SMP is rocket-science level for me yet.
diff --git a/sched/sched/sched_unlock.c b/sched/sched/sched_unlock.c
index 4c7d681454..15fc39b546 100644
--- a/sched/sched/sched_unlock.c
+++ b/sched/sched/sched_unlock.c
@@ -65,13 +65,14 @@ void sched_unlock(void)
DEBUGASSERT(rtcb == NULL || rtcb->lockcount > 0);
- /* Check if the lock counter has decremented to zero. If so,
- * then pre-emption has been re-enabled.
- */
-
- if (rtcb != NULL && --rtcb->lockcount == 0)
+ if (rtcb != NULL && rtcb->lockcount > 1)
+ {
+ rtcb->lockcount--;
+ }
+ else if (rtcb != NULL && rtcb->lockcount == 1)
{
irqstate_t flags = enter_critical_section_wo_note();
+ rtcb->lockcount = 0;
/* Note that we no longer have pre-emption disabled. */
--
2.49.0
On 4/22/25 14:32, hujun260 wrote:
It seems to have nothing to do with the race condition, and since the rtcb is this_task, it
will only be modified by one CPU.<br/><br/>As for why your modification can
solve the problem, I haven't figured it out yet. Can you further analyze the reasons for
the failure to boot?
At 2025-04-22 13:25:13, "Serg Podtynnyi" <s...@podtynnyi.com.INVALID> wrote:
Hi All, Gregory, Sebastien,
I'm porting NuttX on rp2350(pico2 board inside ClockWork PicoCalc) and
having trouble getting SMP (2-core) config running
without patching the sched lock/unlock routines.
I am looking at the commit
https://github.com/apache/nuttx/commit/914ae532e68bf4ca75c758d6f541a1d2fcdce8c3
and reverting it helps to boot the system.
This the the patch to make it work for me, I updated the current
lock/unlock by moving the enter_critical_section above the access to
rtcb->lockcount
Do you think it could be the case of a race condition with rtcb->lockcount ?
PS
It's almost 11 years since I last touched NuttX - it's a please to work
with it again.
From 86fa0a65fdd37804154faf3db52e2826281cdfbd Mon Sep 17 00:00:00 2001
From: Serg Podtynnyi <s...@podtynnyi.com>
Date: Tue, 22 Apr 2025 11:37:48 +0700
Subject: sched: update lock/unlock critical section entry
Level up enter_critical_section in sched lock/unlock to cover
rtcb->lockcount access
Signed-off-by: Serg Podtynnyi <s...@podtynnyi.com>
---
sched/sched/sched_lock.c | 4 ++--
sched/sched/sched_unlock.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/sched/sched/sched_lock.c b/sched/sched/sched_lock.c
index d8f75e7c90..9cc8da3df4 100644
--- a/sched/sched/sched_lock.c
+++ b/sched/sched/sched_lock.c
@@ -82,18 +82,18 @@ void sched_lock(void)
* operations on this thread (on any CPU)
*/
+ irqstate_t flags = enter_critical_section_wo_note();
if (rtcb != NULL && rtcb->lockcount++ == 0)
{
#if (CONFIG_SCHED_CRITMONITOR_MAXTIME_PREEMPTION >= 0) || \
defined(CONFIG_SCHED_INSTRUMENTATION_PREEMPTION)
- irqstate_t flags = enter_critical_section_wo_note();
/* Note that we have pre-emption locked */
nxsched_critmon_preemption(rtcb, true, return_address(0));
sched_note_preemption(rtcb, true);
- leave_critical_section_wo_note(flags);
#endif
}
+ leave_critical_section_wo_note(flags);
}
}
diff --git a/sched/sched/sched_unlock.c b/sched/sched/sched_unlock.c
index 4c7d681454..d21e007587 100644
--- a/sched/sched/sched_unlock.c
+++ b/sched/sched/sched_unlock.c
@@ -69,9 +69,9 @@ void sched_unlock(void)
* then pre-emption has been re-enabled.
*/
+ irqstate_t flags = enter_critical_section_wo_note();
if (rtcb != NULL && --rtcb->lockcount == 0)
{
- irqstate_t flags = enter_critical_section_wo_note();
/* Note that we no longer have pre-emption disabled. */
@@ -162,7 +162,7 @@ void sched_unlock(void)
}
#endif
- leave_critical_section_wo_note(flags);
}
+ leave_critical_section_wo_note(flags);
}
}
--
2.49.0
--
Serg Podtynnyi
-- Serg Podtynnyi
