Re: FAILED: patch "[PATCH] mm/filemap.c: fix NULL pointer in page_cache_tree_insert()" failed to apply to 4.4-stable tree

[Michal Hocko <mhocko@kernel.org>]

On Sun 22-04-18 02:52:40, Nathan Chancellor wrote:
> On Sun, Apr 22, 2018 at 11:33:42AM +0200, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 4.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> > 
> > thanks,
> > 
> > greg k-h
> > 
> > ------------------ original commit in Linus's tree ------------------
> > 
> > From abc1be13fd113ddef5e2d807a466286b864caed3 Mon Sep 17 00:00:00 2001
> > From: Matthew Wilcox <mawilcox@microsoft.com>
> > Date: Fri, 20 Apr 2018 14:56:20 -0700
> > Subject: [PATCH] mm/filemap.c: fix NULL pointer in page_cache_tree_insert()
> > 
> > f2fs specifies the __GFP_ZERO flag for allocating some of its pages.
> > Unfortunately, the page cache also uses the mapping's GFP flags for
> > allocating radix tree nodes.  It always masked off the __GFP_HIGHMEM
> > flag, and masks off __GFP_ZERO in some paths, but not all.  That causes
> > radix tree nodes to be allocated with a NULL list_head, which causes
> > backtraces like:
> > 
> >   __list_del_entry+0x30/0xd0
> >   list_lru_del+0xac/0x1ac
> >   page_cache_tree_insert+0xd8/0x110
> > 
> > The __GFP_DMA and __GFP_DMA32 flags would also be able to sneak through
> > if they are ever used.  Fix them all by using GFP_RECLAIM_MASK at the
> > innermost location, and remove it from earlier in the callchain.
> > 
> > Link: http://lkml.kernel.org/r/20180411060320.14458-2-willy@infradead.org
> > Fixes: 449dd6984d0e ("mm: keep page cache radix tree nodes in check")
> > Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
> > Reported-by: Chris Fries <cfries@google.com>
> > Debugged-by: Minchan Kim <minchan@kernel.org>
> > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> > 
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 9276bdb2343c..0604cb02e6f3 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -786,7 +786,7 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
> >  	VM_BUG_ON_PAGE(!PageLocked(new), new);
> >  	VM_BUG_ON_PAGE(new->mapping, new);
> >  
> > -	error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
> > +	error = radix_tree_preload(gfp_mask & GFP_RECLAIM_MASK);
> >  	if (!error) {
> >  		struct address_space *mapping = old->mapping;
> >  		void (*freepage)(struct page *);
> > @@ -842,7 +842,7 @@ static int __add_to_page_cache_locked(struct page *page,
> >  			return error;
> >  	}
> >  
> > -	error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
> > +	error = radix_tree_maybe_preload(gfp_mask & GFP_RECLAIM_MASK);
> >  	if (error) {
> >  		if (!huge)
> >  			mem_cgroup_cancel_charge(page, memcg, false);
> > @@ -1585,8 +1585,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
> >  		if (fgp_flags & FGP_ACCESSED)
> >  			__SetPageReferenced(page);
> >  
> > -		err = add_to_page_cache_lru(page, mapping, offset,
> > -				gfp_mask & GFP_RECLAIM_MASK);
> > +		err = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
> >  		if (unlikely(err)) {
> >  			put_page(page);
> >  			page = NULL;
> > @@ -2387,7 +2386,7 @@ static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
> >  		if (!page)
> >  			return -ENOMEM;
> >  
> > -		ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask & GFP_KERNEL);
> > +		ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
> >  		if (ret == 0)
> >  			ret = mapping->a_ops->readpage(file, page);
> >  		else if (ret == -EEXIST)
> > 
> 
> It looks like c20cd45eb017 ("mm: allow GFP_{FS,IO} for page_cache_read
> page cache allocation") came in during 4.5 and reorganized a few things
> around the last section.

right

> If you pick that commit then this one, it will be clean (just tested on
> 4.4.128).

Or simply patch all radix_tree_*preload calls to restrict their gfp mask
to GFP_RECLAIM_MASK. Or even simpler to hook into
__radix_tree_preload...
-- 
Michal Hocko
SUSE Labs