Messages in this thread | | | Date | Sun, 26 Feb 2023 10:22:40 -0800 | From | Boqun Feng <> | Subject | Re: [PATCH 5/6] locking/rwsem: Unify wait loop |
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On Sun, Feb 26, 2023 at 01:01:10PM +0100, Peter Zijlstra wrote: > On Thu, Feb 23, 2023 at 05:33:53PM -0800, Boqun Feng wrote: > > On Thu, Feb 23, 2023 at 11:31:47AM -0800, Boqun Feng wrote: > > [..] > > > > +#define waiter_type(_waiter, _r, _w) \ > > > > + ((_waiter)->type == RWSEM_WAITING_FOR_READ ? (_r) : (_w)) > > > > + > > > > +static __always_inline struct rw_semaphore * > > > > +rwsem_waiter_wait(struct rw_semaphore *sem, struct rwsem_waiter *waiter, int state) > > > > +{ > > > > + trace_contention_begin(sem, waiter_type(waiter, LCB_F_READ, LCB_F_WRITE)); > > > > + > > > > + /* wait to be given the lock */ > > > > + for (;;) { > > > > + set_current_state(state); > > > > + if (!smp_load_acquire(&waiter->task)) { > > > > + /* Matches rwsem_waiter_wake()'s smp_store_release(). */ > > > > + break; > > > > + } > > > > + if (signal_pending_state(state, current)) { > > > > + raw_spin_lock_irq(&sem->wait_lock); > > > > > > Move the below __set_current_state(TASK_RUNNING)s up here? I think we > > > need the preemption protection when changing the task state here. > > > > > > > Nevermind since we have the preemption protection for the whole > > function... but merging two __set_current_state()s into one still looks > > good. > > Even if it were not; I still don't understand the concern. Preemption > ignores task state.
Because I missed the exact thing you just mentioned... ;-)
I was worried about the following case:
ttwu(); set_current_state(TASK_UNINTERRUPTIBLE); .... <preemption enable> <preempted> preempt_schedule_irq(): __schedule(...): deactivate_task(); // Wakeup missed.
However this is not true, since __schedule() in preempt_schedule_irq() is a SM_PREEMPT one.
Sorry for the noise then. But good for me to revisit these stuffs ;-)
Regards, Boqun
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