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Message-ID: <20190503152125.GH2623@hirez.programming.kicks-ass.net> Date: Fri, 3 May 2019 17:21:25 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Waiman Long <longman@...hat.com> Cc: Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org, x86@...nel.org, Davidlohr Bueso <dave@...olabs.net>, Linus Torvalds <torvalds@...ux-foundation.org>, Tim Chen <tim.c.chen@...ux.intel.com>, huang ying <huang.ying.caritas@...il.com> Subject: Re: [PATCH-tip v7 12/20] locking/rwsem: Clarify usage of owner's nonspinaable bit On Sun, Apr 28, 2019 at 05:25:49PM -0400, Waiman Long wrote: > Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an > anonymous owner - readers or an anonymous writer. The setting of this > anonymous bit is used as an indicator that optimistic spinning cannot > be done on this rwsem. > > With the upcoming reader optimistic spinning patches, a reader-owned > rwsem can be spinned on for a limit period of time. We still need > this bit to indicate a rwsem is nonspinnable, but not setting this > bit loses its meaning that the owner is known. So rename the bit > to RWSEM_NONSPINNABLE to clarify its meaning. > > This patch also fixes a DEBUG_RWSEMS_WARN_ON() bug in __up_write(). > > Signed-off-by: Waiman Long <longman@...hat.com> > --- > include/linux/rwsem.h | 2 +- > kernel/locking/rwsem.c | 43 +++++++++++++++++++++--------------------- > 2 files changed, 22 insertions(+), 23 deletions(-) > > diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h > index 148983e21d47..bb76e82398b2 100644 > --- a/include/linux/rwsem.h > +++ b/include/linux/rwsem.h > @@ -50,7 +50,7 @@ struct rw_semaphore { > }; > > /* > - * Setting bit 1 of the owner field but not bit 0 will indicate > + * Setting all bits of the owner field except bit 0 will indicate > * that the rwsem is writer-owned with an unknown owner. > */ > #define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-2L) As you know, I'm trying to kill that :-)
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