linux-kernel - Re: [PATCH 1/6] mm: khugepaged: fix radix tree node leak in shmem collapse error path

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Message-ID: <20161114164822.GB5141@cmpxchg.org>
Date:   Mon, 14 Nov 2016 11:48:22 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 1/6] mm: khugepaged: fix radix tree node leak in shmem
 collapse error path

On Mon, Nov 14, 2016 at 10:52:50AM -0500, Johannes Weiner wrote:
> On Mon, Nov 14, 2016 at 05:29:02PM +0300, Kirill A. Shutemov wrote:
> > @@ -1400,7 +1400,9 @@ static void collapse_shmem(struct mm_struct *mm,
> >  					PAGE_SIZE, 0);
> >  
> >  		spin_lock_irq(&mapping->tree_lock);
> > -
> > +		slot = radix_tree_lookup_slot(&mapping->page_tree, index);
> > +		VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
> > +					&mapping->tree_lock), page);
> >  		VM_BUG_ON_PAGE(page_mapped(page), page);
> 
> That looks good to me. The slot may get relocated, but the content
> shouldn't change with the page locked.
> 
> Are you going to send a full patch with changelog and sign-off? If so,
> please add:
> 
> Acked-by: Johannes Weiner <hannes@...xchg.org>

Just to clarify, this is in addition to my radix_tree_iter_next()
change. The iterator still needs to be reloaded because the number of
valid slots that come after the current one can change as well.