Re: [PATCH 4/4] maple_tree: fix potential allocation failure even has memory

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Wei Yang <richard.weiyang@gmail.com> [241010 21:27]:
> 
> Related fix has been posted, but not merged yet.
> 
> lkml.kernel.org/r/20240626160631.3636515-1-Liam.Howlett@oracle.com
> 
> May drop this one.

Yes, thanks.  This can be dropped in favour of the other commit.

> 
> On Tue, Sep 24, 2024 at 12:39:54PM +0000, Wei Yang wrote:
> >We got an rare case when mas_node_count() would fail even there is
> >enough memory.
> >
> >The reason is the maple_alloc grows downward. And when hit a full
> >maple_alloc, the max_req would be 0. This leads to mt_alloc_bulk()
> >return 0, which means failure here.
> >
> >For example, here is the test code:
> >
> >	expect = MAPLE_ALLOC_SLOTS + 1;
> >	mas_node_count(&ms, expect);
> >	pr_info("expect %d allocated %lu\n", expect, mas_allocated(&ms));
> >	expect = MAPLE_ALLOC_SLOTS * 2 + 2;
> >	mas_node_count(&ms, expect);
> >	pr_info("expect %d allocated %lu\n", expect, mas_allocated(&ms));
> >
> >We will get the following output, which shows we fail to allocate the
> >required number of nodes.
> >
> >	expect 31 allocated 31
> >        expect 62 allocated 61
> >
> >The straight forward way to fix it is go down one level more.
> >
> >Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> >CC: Liam R. Howlett <Liam.Howlett@Oracle.com>
> >CC: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> >---
> > lib/maple_tree.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> >diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> >index 1cbc5f7ca40d..dd33d0793dd1 100644
> >--- a/lib/maple_tree.c
> >+++ b/lib/maple_tree.c
> >@@ -1253,8 +1253,10 @@ static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
> > 	}
> > 
> > 	node = mas->alloc;
> >-	while (requested) {
> >+	for (; requested; node = node->slot[0]) {
> > 		max_req = MAPLE_ALLOC_SLOTS - node->node_count;
> >+		if (unlikely(!max_req))
> >+			continue;
> > 		slots = (void **)&node->slot[node->node_count];
> > 		max_req = min(requested, max_req);
> > 		count = mt_alloc_bulk(gfp, max_req, slots);
> >@@ -1268,7 +1270,6 @@ static inline void mas_alloc_nodes(struct ma_state *mas, gfp_t gfp)
> > 
> > 		node->node_count += count;
> > 		allocated += count;
> >-		node = node->slot[0];
> > 		requested -= count;
> > 	}
> > 	mas->alloc->total = allocated;
> >-- 
> >2.34.1
> 
> -- 
> Wei Yang
> Help you, Help me
>