linux-kernel - Re: [PATCH] fs/netfs: Remove redundant use of smp

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Message-ID: <2011011.1733558696@warthog.procyon.org.uk>
Date: Sat, 07 Dec 2024 08:04:56 +0000
From: David Howells <dhowells@...hat.com>
To: Akira Yokosawa <akiyks@...il.com>
Cc: dhowells@...hat.com, zilin@....edu.cn, jianhao.xu@....edu.cn,
    jlayton@...nel.org, linux-fsdevel@...r.kernel.org,
    linux-kernel@...r.kernel.org, netfs@...ts.linux.dev,
    mjguzik@...il.com
Subject: Re: [PATCH] fs/netfs: Remove redundant use of smp_rmb()

Akira Yokosawa <akiyks@...il.com> wrote:

> Are you sure removing the smp_rmb() is realy the right thing to do?

The wait_on_bit*() class functions, e.g.:

	wait_on_bit(unsigned long *word, int bit, unsigned mode)
	{
		might_sleep();
		if (!test_bit_acquire(bit, word))
			return 0;
		return out_of_line_wait_on_bit(word, bit,
					       bit_wait,
					       mode);
	}

now unconditionally includes an appropriate barrier on the test_bit(), so the
smp_rmb() should be unnecessary, though netfslib should probably be using
clear_and_wake_up_bit().

Probably we need to update the doc to reflect this.

David