linux-kernel - [PATCH] mm, kasan: fix __GFP_BITS_SHIFT definition breaking LOCKDEP

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Date:   Sun, 27 Mar 2022 19:00:23 +0200
From:   andrey.konovalov@...ux.dev
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH] mm, kasan: fix __GFP_BITS_SHIFT definition breaking LOCKDEP

From: Andrey Konovalov <andreyknvl@...gle.com>

KASAN changes that added new GFP flags mistakenly updated __GFP_BITS_SHIFT
as the total number of GFP bits instead of as a shift used to define
__GFP_BITS_MASK.

This broke LOCKDEP, as __GFP_BITS_MASK now gets the 25th bit enabled
instead of the 28th for __GFP_NOLOCKDEP.

Update __GFP_BITS_SHIFT to always count KASAN GFP bits.

In the future, we could handle all combinations of KASAN and LOCKDEP to
occupy as few bits as possible. For now, we have enough GFP bits to be
inefficient in this quick fix.

Fixes: 9353ffa6e9e9 ("kasan, page_alloc: allow skipping memory init for HW_TAGS")
Fixes: 53ae233c30a6 ("kasan, page_alloc: allow skipping unpoisoning for HW_TAGS")
Fixes: f49d9c5bb15c ("kasan, mm: only define ___GFP_SKIP_KASAN_POISON with HW_TAGS")
Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 include/linux/gfp.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 0fa17fb85de5..761f8f1885c7 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -264,9 +264,7 @@ struct vm_area_struct;
 #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
 
 /* Room for N __GFP_FOO bits */
-#define __GFP_BITS_SHIFT (24 +						\
-			  3 * IS_ENABLED(CONFIG_KASAN_HW_TAGS) +	\
-			  IS_ENABLED(CONFIG_LOCKDEP))
+#define __GFP_BITS_SHIFT (27 + IS_ENABLED(CONFIG_LOCKDEP))
 #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
 
 /**
-- 
2.25.1