linux-kernel - Re: [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG

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Date:   Tue, 23 Mar 2021 22:06:04 +0000
From:   David Howells <dhowells@...hat.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     dhowells@...hat.com, Matthew Wilcox <willy@...radead.org>,
        Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Alexander Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...hat.com>,
        David Wysochanski <dwysocha@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG_fscache

David Howells <dhowells@...hat.com> wrote:

> > > -	wait_on_page_writeback(page);
> > > +	if (wait_on_page_writeback_killable(page) < 0)
> > > +		return VM_FAULT_RETRY | VM_FAULT_LOCKED;
> > 
> > You forgot to unlock the page.
> 
> Do I need to?  Doesn't VM_FAULT_LOCKED indicate that to the caller?  Or is it
> impermissible to do it like that?

Looks like, yes, I do need to.  VM_FAULT_LOCKED is ignored if RETRY is given.

David