linux-kernel - Re: [PATCH v10 22/33] mm/filemap: Add __folio_lock_or

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Date:   Tue, 18 May 2021 14:35:46 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Jeff Layton <jlayton@...nel.org>
Subject: Re: [PATCH v10 22/33] mm/filemap: Add __folio_lock_or_retry

On Tue, May 18, 2021 at 12:38:46PM +0200, Vlastimil Babka wrote:
> > -int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
> > +int __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
> >  			 unsigned int flags)
> >  {
> > -	struct folio *folio = page_folio(page);
> > -
> >  	if (fault_flag_allow_retry_first(flags)) {
> >  		/*
> >  		 * CAUTION! In this case, mmap_lock is not released
> 
> A bit later in this branch, 'page' is accessed, but it no longer exists. And
> thus as expected, it doesn't compile. Assuming it's fixed later, but
> bisectability etc...

Oops.  Thanks for catching that; I've reordered this patch and the
folio_wait_locked() patch, which makes the entire problem go away.