linux-kernel - Re: [PATCH 1/5] locking: Add rwsem_is_write

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Message-ID: <ZPolpUuCiGT/5PLO@casper.infradead.org>
Date:   Thu, 7 Sep 2023 20:33:57 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Chandan Babu R <chandan.babu@...cle.com>,
        "Darrick J . Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org
Subject: Re: [PATCH 1/5] locking: Add rwsem_is_write_locked()

On Thu, Sep 07, 2023 at 02:05:54PM -0400, Waiman Long wrote:
> On 9/7/23 13:47, Matthew Wilcox (Oracle) wrote:
> > +static inline int rwsem_is_write_locked(struct rw_semaphore *sem)
> > +{
> > +	return atomic_long_read(&sem->count) & 1 /* RWSEM_WRITER_LOCKED */;
> > +}
> 
> I would prefer you move the various RWSEM_* count bit macros from
> kernel/locking/rwsem.c to under the !PREEMPT_RT block and directly use
> RWSEM_WRITER_LOCKED instead of hardcoding a value of 1.

Just to be clear, you want the ~50 lines from:

/*
 * On 64-bit architectures, the bit definitions of the count are:
...
#define RWSEM_READ_FAILED_MASK  (RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\
                                 RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)

moved from rwsem.c to rwsem.h?

Or just these four lines:

#define RWSEM_WRITER_LOCKED     (1UL << 0)
#define RWSEM_FLAG_WAITERS      (1UL << 1)
#define RWSEM_FLAG_HANDOFF      (1UL << 2)
#define RWSEM_FLAG_READFAIL     (1UL << (BITS_PER_LONG - 1))