mm, kasan: fix __GFP_BITS_SHIFT definition breaking LOCKDEP

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.

Link: https://lkml.kernel.org/r/462ff52742a1fcc95a69778685737f723ee4dfb3.1648400273.git.andreyknvl@google.com
Fixes: 9353ffa ("kasan, page_alloc: allow skipping memory init for HW_TAGS")
Fixes: 53ae233 ("kasan, page_alloc: allow skipping unpoisoning for HW_TAGS")
Fixes: f49d9c5 ("kasan, mm: only define ___GFP_SKIP_KASAN_POISON with HW_TAGS")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: xairy

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))
 
 /**