musl - MSB in rwlock?

Message-ID: <20190122202847.GB23924@voyager>
Date: Tue, 22 Jan 2019 21:28:47 +0100
From: Markus Wichmann <nullplan@....net>
To: musl@...ts.openwall.com
Subject: MSB in rwlock?

Hi all,

would someone kindly explain what the highest bit in the rwlock value is
doing? As far as I can see, it is set whenever one of the locking
functions enters a contended case, and cleared when the unlock function
sets the lock to 0 (so when the last reader or the writer unlocks the
rwlock). But at any other point the bit is masked out, AFAICS. So what
is it doing? Or is it just a vestige that can be done away with?

Ciao,
Markus

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