linux-kernel - [PATCH v4 05/11] mm: do not split a folio if it has minimum folio order requirement

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Message-Id: <20240425113746.335530-6-kernel@pankajraghav.com>
Date: Thu, 25 Apr 2024 13:37:40 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: willy@...radead.org,
	djwong@...nel.org,
	brauner@...nel.org,
	david@...morbit.com,
	chandan.babu@...cle.com,
	akpm@...ux-foundation.org
Cc: linux-fsdevel@...r.kernel.org,
	hare@...e.de,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-xfs@...r.kernel.org,
	mcgrof@...nel.org,
	gost.dev@...sung.com,
	p.raghav@...sung.com
Subject: [PATCH v4 05/11] mm: do not split a folio if it has minimum folio order requirement

From: Pankaj Raghav <p.raghav@...sung.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@...sung.com>
Signed-off-by: Luis Chamberlain <mcgrof@...nel.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