linux-ext4 - Re: [PATCH 2/7] mm: Protect operations adding pages to page cache with i_mapping

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Date:   Tue, 13 Apr 2021 15:56:32 +0200
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        Ted Tso <tytso@....edu>, Amir Goldstein <amir73il@...il.com>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 2/7] mm: Protect operations adding pages to page cache
 with i_mapping_lock

On Tue 13-04-21 13:57:46, Christoph Hellwig wrote:
> >  	if (error == AOP_TRUNCATED_PAGE)
> >  		put_page(page);
> > +	up_read(&mapping->host->i_mapping_sem);
> >  	return error;
> 
> Please add an unlock_mapping label above this up_read and consolidate
> most of the other unlocks by jumping there (put_and_wait_on_page_locked
> probablt can't use it).

Yeah, I've actually simplified the labels even a bit more like:

...
        error = filemap_read_page(iocb->ki_filp, mapping, page);
        goto unlock_mapping;
unlock:
        unlock_page(page);
unlock_mapping:
        up_read(&mapping->host->i_mapping_sem);
        if (error == AOP_TRUNCATED_PAGE)
                put_page(page);
        return error;

and everything now jumps to either unlock or unlock_mapping (except for
put_and_wait_on_page_locked() case).

> >  truncated:
> >  	unlock_page(page);
> > @@ -2309,6 +2324,7 @@ static int filemap_update_page(struct kiocb *iocb,
> >  	return AOP_TRUNCATED_PAGE;
> 
> The trunated case actually seems to miss the unlock.
> 
> Similarly I think filemap_fault would benefit from a common
> unlock path.

Right, thanks for catching that!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR