Messages in this thread Patch in this message | | | Date | Thu, 09 Sep 2021 12:59:16 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 1/4] sched/wakeup: Strengthen current_save_and_set_rtlock_wait_state() |
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While looking at current_save_and_set_rtlock_wait_state() I'm thinking it really ought to use smp_store_mb(), because something like:
current_save_and_set_rtlock_wait_state(); for (;;) { if (try_lock()) break;
raw_spin_unlock_irq(&lock->wait_lock); schedule(); raw_spin_lock_irq(&lock->wait_lock);
set_current_state(TASK_RTLOCK_WAIT); } current_restore_rtlock_saved_state();
which is the advertised usage in the comment, is actually broken, since trylock() will only need a load-acquire in general and that could be re-ordered against the state store, which could lead to a missed wakeup -> BAD (tm).
While there, make them consistent with the IRQ usage in set_special_state().
Fixes: 5f220be21418 ("sched/wakeup: Prepare for RT sleeping spin/rwlocks") Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- include/linux/sched.h | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-)
--- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -245,7 +245,8 @@ struct task_group; * if (try_lock()) * break; * raw_spin_unlock_irq(&lock->wait_lock); - * schedule_rtlock(); + * if (!cond) + * schedule_rtlock(); * raw_spin_lock_irq(&lock->wait_lock); * set_current_state(TASK_RTLOCK_WAIT); * } @@ -253,22 +254,24 @@ struct task_group; */ #define current_save_and_set_rtlock_wait_state() \ do { \ - lockdep_assert_irqs_disabled(); \ - raw_spin_lock(¤t->pi_lock); \ + unsigned long flags; /* may shadow */ \ + \ + raw_spin_lock_irqsave(¤t->pi_lock, flags); \ current->saved_state = current->__state; \ debug_rtlock_wait_set_state(); \ - WRITE_ONCE(current->__state, TASK_RTLOCK_WAIT); \ - raw_spin_unlock(¤t->pi_lock); \ + smp_store_mb(current->__state, TASK_RTLOCK_WAIT); \ + raw_spin_unlock_irqrestore(¤t->pi_lock, flags); \ } while (0); #define current_restore_rtlock_saved_state() \ do { \ - lockdep_assert_irqs_disabled(); \ - raw_spin_lock(¤t->pi_lock); \ + unsigned long flags; /* may shadow */ \ + \ + raw_spin_lock_irqsave(¤t->pi_lock, flags); \ debug_rtlock_wait_restore_state(); \ WRITE_ONCE(current->__state, current->saved_state); \ current->saved_state = TASK_RUNNING; \ - raw_spin_unlock(¤t->pi_lock); \ + raw_spin_unlock_irqrestore(¤t->pi_lock, flags); \ } while (0); #define get_current_state() READ_ONCE(current->__state)
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