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Date: Wed, 16 May 2018 13:59:06 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v4 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED
 flag
Message-ID: <20180516115906.GF12217@hirez.programming.kicks-ass.net>
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 <20180516104829.GA24332@redhat.com>
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On Wed, May 16, 2018 at 12:48:30PM +0200, Oleg Nesterov wrote:
> > +static inline bool is_rwsem_owner_spinnable(struct task_struct *owner)
> >  {
> > -	return owner && owner != RWSEM_READER_OWNED;
> > +	return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED);
> >  }
> 
> Perhaps you should add __attribute__(aligned) to struct rw_semaphore then...
> 
> I don't think it is really needed, but see the comment under struct address_space.

Luckily we just dropped CRIS support, but yeah, who knows if some other
dodgy arch also doesn't properly align things.

>>From a quick test, m68k is the only odd one, it seems to align pointers
on 2 bytes.