linux-kernel - Re: [GIT PULL] dax fixes for 4.20-rc6

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Date:   Sun, 9 Dec 2018 10:01:51 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     dan.j.williams@...el.com
Cc:     Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        linux-nvdimm@...ts.01.org
Subject: Re: [GIT PULL] dax fixes for 4.20-rc6

On Sat, Dec 8, 2018 at 10:26 PM Williams, Dan J
<dan.j.williams@...el.com> wrote:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm tags/dax-fixes-4.20-rc6

What's going on with the odd non-exclusive exclusive wait?

        prepare_to_wait_exclusive(wq, &ewait.wait, TASK_UNINTERRUPTIBLE);
        ...
        /*
         * Entry lock waits are exclusive. Wake up the next waiter since
         * we aren't sure we will acquire the entry lock and thus wake
         * the next waiter up on unlock.
         */
        if (waitqueue_active(wq))
                __wake_up(wq, TASK_NORMAL, 1, &ewait.key);

that seems to make little or no sense.

Why isn't that prepare_to_wait_exclusive() just a regular
prepare_to_wait(), and then the whole "let's wake up anybody else" can
be removed?

I've pulled it, but am awaiting explanation of what looks like some
pretty crazy code. I *suspect* it's a copy-and-paste situation where
you took the exclusive wait from somewhere else.

                Linus