linux-kernel - Re: [PATCH 3/6] locking/rwsem: Rework writer wakeup

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Date:   Sun, 26 Feb 2023 17:51:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     longman@...hat.com, mingo@...hat.com, will@...nel.org
Cc:     linux-kernel@...r.kernel.org, boqun.feng@...il.com
Subject: Re: [PATCH 3/6] locking/rwsem: Rework writer wakeup

On Sun, Feb 26, 2023 at 04:04:35PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 23, 2023 at 01:26:45PM +0100, Peter Zijlstra wrote:
> > @@ -1072,7 +1067,7 @@ rwsem_down_read_slowpath(struct rw_semap
> >  	for (;;) {
> >  		set_current_state(state);
> >  		if (!smp_load_acquire(&waiter.task)) {
> > -			/* Matches rwsem_mark_wake()'s smp_store_release(). */
> > +			/* Matches rwsem_waiter_wake()'s smp_store_release(). */
> >  			break;
> >  		}
> >  		if (signal_pending_state(state, current)) {
> > @@ -1143,54 +1138,36 @@ rwsem_down_write_slowpath(struct rw_sema
> >  	} else {
> >  		atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
> 
> Found it; if we remove the try_write_lock below, then at least this
> new-waiter path needs to still do a trylock.
> 
> Let me go test the other patches on top of all this and push out a fresh
> set if that all still works.

queue.git locking/core

We'll see what the robots make of it.