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kernel/sched: Fix lockless ordering in halt_thread()

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We've had threads spinning on the thread state bits, but weren't being
careful to ensure that those bits were the last things seen to change
in a halting thread.  Move it to the end, and add a barrier for
correctness.

Signed-off-by: Andy Ross <andyross@google.com>
This commit is contained in:
Andy Ross 2024-04-19 15:08:55 -07:00 • committed by Carles Cufí
commit 02b24911f7
1 changed files with 8 additions and 1 deletions
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9
kernel/sched.c
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@ -195,6 +195,7 @@ static inline bool is_halting(struct k_thread *thread)
/* Clear the halting bits (_THREAD_ABORTING and _THREAD_SUSPENDING) */ /* Clear the halting bits (_THREAD_ABORTING and _THREAD_SUSPENDING) */
static inline void clear_halting(struct k_thread *thread) static inline void clear_halting(struct k_thread *thread)
{ {
barrier_dmem_fence_full(); /* Other cpus spin on this locklessly! */
thread->base.thread_state &= ~(_THREAD_ABORTING | _THREAD_SUSPENDING); thread->base.thread_state &= ~(_THREAD_ABORTING | _THREAD_SUSPENDING);
} }
@ -1296,7 +1297,6 @@ static void halt_thread(struct k_thread *thread, uint8_t new_state)
*/ */
if ((thread->base.thread_state & new_state) == 0U) { if ((thread->base.thread_state & new_state) == 0U) {
thread->base.thread_state |= new_state; thread->base.thread_state |= new_state;
clear_halting(thread);
if (z_is_thread_queued(thread)) { if (z_is_thread_queued(thread)) {
dequeue_thread(thread); dequeue_thread(thread);
} }
@ -1324,6 +1324,7 @@ static void halt_thread(struct k_thread *thread, uint8_t new_state)
update_cache(1); update_cache(1);
if (new_state == _THREAD_SUSPENDED) { if (new_state == _THREAD_SUSPENDED) {
clear_halting(thread);
return; return;
} }
@ -1365,6 +1366,12 @@ static void halt_thread(struct k_thread *thread, uint8_t new_state)
if (dummify && !IS_ENABLED(CONFIG_ARCH_POSIX)) { if (dummify && !IS_ENABLED(CONFIG_ARCH_POSIX)) {
z_dummy_thread_init(&_thread_dummy); z_dummy_thread_init(&_thread_dummy);
} }
/* Finally update the halting thread state, on which
* other CPUs might be spinning (see
* thread_halt_spin()).
*/
clear_halting(thread);
} }
} }