linux-kernel - [RFC PATCH] mm/slab: Avoid build bug for calls to kmalloc with a large constant

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Message-ID: <44312f4a-8b9c-49ce-9277-5873a94ca1bb@oracle.com>
Date: Fri, 1 Nov 2024 15:16:21 -0500
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: [RFC PATCH] mm/slab: Avoid build bug for calls to kmalloc with a
 large constant

When boot-time page size is enabled, the test against KMALLOC_MAX_CACHE_SIZE
is no longer optimized out with a constant size, so a build bug may
occur on a path that won't be reached.

Found compiling drivers/net/ethernet/qlogic/qed/qed_sriov.c

Signed-off-by: Dave Kleikamp <dave.kleikamp@...cle.com>
---

Ryan,

Please consider incorporating this fix or something similar into your
mm patch in the boot-time pages size patches.

  include/linux/slab.h | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 9848296ca6ba..a4c7507ab8ec 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -685,7 +685,8 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
  	if (size <= 1024 * 1024) return 20;
  	if (size <=  2 * 1024 * 1024) return 21;
  
-	if (!IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES) && size_is_constant)
+	if (!IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE) &&
+	    !IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES) && size_is_constant)
  		BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");
  	else
  		BUG();
-- 
2.47.0