linux-kernel - Re: [PATCH] fscache: Use wake_up_var() to wake up pending volume acquisition

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Message-ID: <2308529.1670585211@warthog.procyon.org.uk>
Date:   Fri, 09 Dec 2022 11:26:51 +0000
From:   David Howells <dhowells@...hat.com>
To:     Hou Tao <houtao@...weicloud.com>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com,
        Jeff Layton <jlayton@...nel.org>, linux-erofs@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        "houtao1@...wei.com" <houtao1@...wei.com>
Subject: Re: [PATCH] fscache: Use wake_up_var() to wake up pending volume acquisition

Hou Tao <houtao@...weicloud.com> wrote:

> >  			clear_bit(FSCACHE_VOLUME_ACQUIRE_PENDING, &cursor->flags);

Maybe this should be clear_bit_unlock() instead.

And I wonder if:

	set_bit(FSCACHE_VOLUME_ACQUIRE_PENDING, &candidate->flags);

in fscache_hash_volume() needs a barrier before it.

> > -			wake_up_bit(&cursor->flags, FSCACHE_VOLUME_ACQUIRE_PENDING);
> > +			/*
> > +			 * Paired with barrier in wait_var_event(). Check
> > +			 * waitqueue_active() and wake_up_var() for details.
> > +			 */
> > +			smp_mb__after_atomic();
> > +			wake_up_var(&cursor->flags);

That doesn't seem right.

wake_up_bit() is more selective, so should be preferred to wake_up_var().

David