linux-kernel - Re: [PATCH] netfs: Fix netfs_page_mkwrite() to check folio->mapping is valid

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Message-ID: <720579.1719268838@warthog.procyon.org.uk>
Date: Mon, 24 Jun 2024 23:40:38 +0100
From: David Howells <dhowells@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: dhowells@...hat.com, Christian Brauner <christian@...uner.io>,
    Jeff Layton <jlayton@...nel.org>, netfs@...ts.linux.dev,
    v9fs@...ts.linux.dev, linux-afs@...ts.infradead.org,
    linux-cifs@...r.kernel.org, linux-mm@...ck.org,
    linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netfs: Fix netfs_page_mkwrite() to check folio->mapping is valid

Matthew Wilcox <willy@...radead.org> wrote:

> >  	if (folio_lock_killable(folio) < 0)
> >  		goto out;
> > +	if (folio->mapping != mapping) {
> > +		ret = VM_FAULT_NOPAGE | VM_FAULT_LOCKED;
> > +		goto out;
> > +	}
> 
> Have you tested this?

I've tried to.  generic/247 can trigger it, but the race happens rarely.

> I'd expect it to throw some VM assertions.

I didn't see any.

I guess VM_FAULT_LOCKED is not universally handled by the caller and that I
should unlock the folio myself instead.

David