From 8850d773703f8114d7c8a2421fd20bde8a558f96 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Sun, 15 Aug 2021 23:28:55 +0200 Subject: [PATCH] locking/ww_mutex: Add RT priority to W/W order RT mutex based ww_mutexes cannot order based on timestamps. They have to order based on priority. Add the necessary decision logic. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20210815211304.847536630@linutronix.de --- kernel/locking/ww_mutex.h | 64 ++++++++++++++++++++++++++++++++++++----------- 1 file changed, 49 insertions(+), 15 deletions(-) diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 7da9890..2dce4f0 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -219,19 +219,54 @@ ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx) } /* - * Determine if context @a is 'after' context @b. IOW, @a is a younger - * transaction than @b and depending on algorithm either needs to wait for - * @b or die. + * Determine if @a is 'less' than @b. IOW, either @a is a lower priority task + * or, when of equal priority, a younger transaction than @b. + * + * Depending on the algorithm, @a will either need to wait for @b, or die. */ static inline bool -__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b) +__ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b) { +/* + * Can only do the RT prio for WW_RT, because task->prio isn't stable due to PI, + * so the wait_list ordering will go wobbly. rt_mutex re-queues the waiter and + * isn't affected by this. + */ +#ifdef WW_RT + /* kernel prio; less is more */ + int a_prio = a->task->prio; + int b_prio = b->task->prio; + + if (rt_prio(a_prio) || rt_prio(b_prio)) { + + if (a_prio > b_prio) + return true; + + if (a_prio < b_prio) + return false; + + /* equal static prio */ + + if (dl_prio(a_prio)) { + if (dl_time_before(b->task->dl.deadline, + a->task->dl.deadline)) + return true; + + if (dl_time_before(a->task->dl.deadline, + b->task->dl.deadline)) + return false; + } + + /* equal prio */ + } +#endif + /* FIFO order tie break -- bigger is younger */ return (signed long)(a->stamp - b->stamp) > 0; } /* - * Wait-Die; wake a younger waiter context (when locks held) such that it can + * Wait-Die; wake a lesser waiter context (when locks held) such that it can * die. * * Among waiters with context, only the first one can have other locks acquired @@ -245,8 +280,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter, if (!ww_ctx->is_wait_die) return false; - if (waiter->ww_ctx->acquired > 0 && - __ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) { + if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) { #ifndef WW_RT debug_mutex_wake_waiter(lock, waiter); #endif @@ -257,10 +291,10 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter, } /* - * Wound-Wait; wound a younger @hold_ctx if it holds the lock. + * Wound-Wait; wound a lesser @hold_ctx if it holds the lock. * - * Wound the lock holder if there are waiters with older transactions than - * the lock holders. Even if multiple waiters may wound the lock holder, + * Wound the lock holder if there are waiters with more important transactions + * than the lock holders. Even if multiple waiters may wound the lock holder, * it's sufficient that only one does. */ static bool __ww_mutex_wound(struct MUTEX *lock, @@ -287,7 +321,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock, if (!owner) return false; - if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) { + if (ww_ctx->acquired > 0 && __ww_ctx_less(hold_ctx, ww_ctx)) { hold_ctx->wounded = 1; /* @@ -306,8 +340,8 @@ static bool __ww_mutex_wound(struct MUTEX *lock, } /* - * We just acquired @lock under @ww_ctx, if there are later contexts waiting - * behind us on the wait-list, check if they need to die, or wound us. + * We just acquired @lock under @ww_ctx, if there are more important contexts + * waiting behind us on the wait-list, check if they need to die, or wound us. * * See __ww_mutex_add_waiter() for the list-order construction; basically the * list is ordered by stamp, smallest (oldest) first. @@ -421,7 +455,7 @@ __ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter, return 0; } - if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx)) + if (hold_ctx && __ww_ctx_less(ctx, hold_ctx)) return __ww_mutex_kill(lock, ctx); /* @@ -479,7 +513,7 @@ __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter, if (!cur->ww_ctx) continue; - if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) { + if (__ww_ctx_less(ww_ctx, cur->ww_ctx)) { /* * Wait-Die: if we find an older context waiting, there * is no point in queueing behind it, as we'd have to -- 2.7.4