From da9647e076d440190fff4b4ee0f4b829dd6e8c4f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 21 Dec 2016 09:05:02 +0100 Subject: [PATCH] sched/completions: Fix complete_all() semantics Documentation/scheduler/completion.txt says this about complete_all(): "calls complete_all() to signal all current and future waiters." Which doesn't strictly match the current semantics. Currently complete_all() is equivalent to UINT_MAX/2 complete() invocations, which is distinctly less than 'all current and future waiters' (enumerable vs innumerable), although it has worked in practice. However, Dmitry had a weird case where it might matter, so change completions to use saturation semantics for complete()/complete_all(). Once done hits UINT_MAX (and complete_all() sets it there) it will never again be decremented. Requested-by: Dmitry Torokhov Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: der.herr@hofr.at Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/completion.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c index 8d0f35debf35..f063a25d4449 100644 --- a/kernel/sched/completion.c +++ b/kernel/sched/completion.c @@ -31,7 +31,8 @@ void complete(struct completion *x) unsigned long flags; spin_lock_irqsave(&x->wait.lock, flags); - x->done++; + if (x->done != UINT_MAX) + x->done++; __wake_up_locked(&x->wait, TASK_NORMAL, 1); spin_unlock_irqrestore(&x->wait.lock, flags); } @@ -51,7 +52,7 @@ void complete_all(struct completion *x) unsigned long flags; spin_lock_irqsave(&x->wait.lock, flags); - x->done += UINT_MAX/2; + x->done = UINT_MAX; __wake_up_locked(&x->wait, TASK_NORMAL, 0); spin_unlock_irqrestore(&x->wait.lock, flags); } @@ -79,7 +80,8 @@ do_wait_for_common(struct completion *x, if (!x->done) return timeout; } - x->done--; + if (x->done != UINT_MAX) + x->done--; return timeout ?: 1; } @@ -280,7 +282,7 @@ bool try_wait_for_completion(struct completion *x) spin_lock_irqsave(&x->wait.lock, flags); if (!x->done) ret = 0; - else + else if (x->done != UINT_MAX) x->done--; spin_unlock_irqrestore(&x->wait.lock, flags); return ret; -- 2.45.2