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

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Message-ID: <20230913085907.GB692@noisy.programming.kicks-ass.net>
Date:   Wed, 13 Sep 2023 10:59:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        Waiman Long <longman@...hat.com>,
        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>,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH 1/5] locking: Add rwsem_is_write_locked()

On Tue, Sep 12, 2023 at 08:27:15AM -0700, Darrick J. Wong wrote:

> I could live with Longman's suggestion of an rwsem_assert_is_locked that
> only exists if DEBUG_RWSEMS is enabled.  Something like:
> 
> #ifdef CONFIG_DEBUG_RWSEMS
> static inline bool __rwsem_assert_is_locked(struct rw_semaphore *rwsem,
> 		const char *file, int line)
> {
> 	bool ret = rwsem_is_locked(rwsem);
> 	if (!ret)
> 		WARN(1, "!rwsem_is_locked(rwsem) at %s line %d", file, line);
> 	return ret;
> }
> #define rwsem_assert_is_locked(r) \
> 	__rwsem_assert_is_locked((r), __FILE__, __LINE__)
> #endif
> 
> and then XFS could do:
> 
> 	ASSERT(rwsem_assert_is_locked(&VFS_I(ip)->i_rwsem));
> 
> Wherein ASSERT is only #defined if CONFIG_XFS_DEBUG, and XFS_DEBUG
> selects DEBUG_RWSEMS, per Longman's suggestion.  That's work for what we
> want it for (simple cheap lock checking) without becoming a general
> lockabuse predicate.

Ack.