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From: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
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Subject: [PATCH v4 05/11] mm: do not split a folio if it has minimum folio order requirement
Date: Thu, 25 Apr 2024 13:37:40 +0200
Message-Id: <20240425113746.335530-6-kernel@pankajraghav.com>
In-Reply-To: <20240425113746.335530-1-kernel@pankajraghav.com>
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From: Pankaj Raghav <p.raghav@samsung.com>

Splitting a larger folio with a base order is supported using
split_huge_page_to_list_to_order() API. However, using that API for LBS
is resulting in an NULL ptr dereference error in the writeback path [1].

Refuse to split a folio if it has minimum folio order requirement until
we can start using split_huge_page_to_list_to_order() API. Splitting the
folio can be added as a later optimization.

[1] https://gist.github.com/mcgrof/d12f586ec6ebe32b2472b5d634c397df

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 mm/huge_memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9859aa4f7553..dadf1e68dbdc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3117,6 +3117,15 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 			goto out;
 		}
 
+		/*
+		 * Do not split if mapping has minimum folio order
+		 * requirement.
+		 */
+		if (mapping_min_folio_order(mapping)) {
+			ret = -EINVAL;
+			goto out;
+		}
+
 		gfp = current_gfp_context(mapping_gfp_mask(mapping) &
 							GFP_RECLAIM_MASK);
 
-- 
2.34.1