[PATCH 3.18.y 4/5] mm/filemap.c: fix NULL pointer in page_cache_tree_insert()

[Harsh Shandilya <harsh@prjkt.io>]

From: Matthew Wilcox <mawilcox@microsoft.com>

Commit abc1be13fd113ddef5e2d807a466286b864caed3 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Harsh Shandilya <harsh@prjkt.io>
---
 mm/filemap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index aafeeefcb00d..6b4bd08bebe1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -468,7 +468,7 @@ 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 *);
@@ -561,7 +561,7 @@ 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);
@@ -1757,7 +1757,7 @@ 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)
-- 
2.15.0.2308.g658a28aa74af