linux-kernel - [PATCH hotfix 6.11] minmax: reduce egregious min/max macro expansion

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Message-ID: <20240911153457.1005227-1-lorenzo.stoakes@oracle.com>
Date: Wed, 11 Sep 2024 16:34:57 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Richard Narron <richard@...zen.com>, Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marcin Wojtas <marcin.s.wojtas@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...nel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: [PATCH hotfix 6.11] minmax: reduce egregious min/max macro expansion

Avoid nested min()/max() which results in egregious macro expansion.

This issue was introduced by commit 867046cc7027 ("minmax: relax check to
allow comparison between unsigned arguments and signed constants") [2].

Work has been done to address the issue of egregious min()/max() macro
expansion in commit 22f546873149 ("minmax: improve macro expansion and type
checking") and related, however it appears that some issues remain on more
tightly constrained systems.

Adjust a few known-bad cases of deeply nested macros to avoid doing so to
mitigate this. Porting the patch first proposed in [1] to Linus's tree.

Running an allmodconfig build using the methodology described in [2] we
observe a 35 MiB reduction in generated code.

The difference is much more significant prior to recent minmax fixes which
were not backported. As per [1] prior these the reduction is more like 200
MiB.

This resolves an issue with slackware 15.0 32-bit compilation as reported
by Richard Narron.

Presumably the min/max fixups would be difficult to backport, this patch
should be easier and fix's Richard's problem in 5.15.

[0]:https://lore.kernel.org/all/b97faef60ad24922b530241c5d7c933c@AcuMS.aculab.com/
[1]:https://lore.kernel.org/lkml/5882b96e-1287-4390-8174-3316d39038ef@lucifer.local/
[2]:https://lore.kernel.org/linux-mm/36aa2cad-1db1-4abf-8dd2-fb20484aabc3@lucifer.local/

Reported-by: Richard Narron <richard@...zen.com>
Closes: https://lore.kernel.org/all/4a5321bd-b1f-1832-f0c-cea8694dc5aa@aaazen.com/
Fixes: 867046cc7027 ("minmax: relax check to allow comparison between unsigned arguments and signed constants")
Cc: stable@...r.kernel.org
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 drivers/net/ethernet/marvell/mvpp2/mvpp2.h    |  2 +-
 .../staging/media/atomisp/pci/sh_css_frac.h   | 26 ++++++++++++++-----
 include/linux/skbuff.h                        |  6 ++++-
 3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
index e809f91c08fb..8b431f90efc3 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
@@ -23,7 +23,7 @@
 /* The PacketOffset field is measured in units of 32 bytes and is 3 bits wide,
  * so the maximum offset is 7 * 32 = 224
  */
-#define MVPP2_SKB_HEADROOM	min(max(XDP_PACKET_HEADROOM, NET_SKB_PAD), 224)
+#define MVPP2_SKB_HEADROOM	clamp_t(int, XDP_PACKET_HEADROOM, NET_SKB_PAD, 224)

 #define MVPP2_XDP_PASS		0
 #define MVPP2_XDP_DROPPED	BIT(0)
diff --git a/drivers/staging/media/atomisp/pci/sh_css_frac.h b/drivers/staging/media/atomisp/pci/sh_css_frac.h
index b90b5b330dfa..a973394c5bc0 100644
--- a/drivers/staging/media/atomisp/pci/sh_css_frac.h
+++ b/drivers/staging/media/atomisp/pci/sh_css_frac.h
@@ -32,12 +32,24 @@
 #define uISP_VAL_MAX		      ((unsigned int)((1 << uISP_REG_BIT) - 1))

 /* a:fraction bits for 16bit precision, b:fraction bits for ISP precision */
-#define sDIGIT_FITTING(v, a, b) \
-	min_t(int, max_t(int, (((v) >> sSHIFT) >> max(sFRACTION_BITS_FITTING(a) - (b), 0)), \
-	  sISP_VAL_MIN), sISP_VAL_MAX)
-#define uDIGIT_FITTING(v, a, b) \
-	min((unsigned int)max((unsigned)(((v) >> uSHIFT) \
-	>> max((int)(uFRACTION_BITS_FITTING(a) - (b)), 0)), \
-	  uISP_VAL_MIN), uISP_VAL_MAX)
+static inline int sDIGIT_FITTING(short v, int a, int b)
+{
+	int fit_shift = sFRACTION_BITS_FITTING(a) - b;
+
+	v >>= sSHIFT;
+	v >>= fit_shift > 0 ? fit_shift : 0;
+
+	return clamp_t(int, v, sISP_VAL_MIN, sISP_VAL_MAX);
+}
+
+static inline unsigned int uDIGIT_FITTING(unsigned int v, int a, int b)
+{
+	int fit_shift = uFRACTION_BITS_FITTING(a) - b;
+
+	v >>= uSHIFT;
+	v >>= fit_shift > 0 ? fit_shift : 0;
+
+	return clamp_t(unsigned int, v, uISP_VAL_MIN, uISP_VAL_MAX);
+}

 #endif /* __SH_CSS_FRAC_H */
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 29c3ea5b6e93..d53b296df504 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3164,7 +3164,11 @@ static inline int pskb_network_may_pull(struct sk_buff *skb, unsigned int len)
  * NET_IP_ALIGN(2) + ethernet_header(14) + IP_header(20/40) + ports(8)
  */
 #ifndef NET_SKB_PAD
-#define NET_SKB_PAD	max(32, L1_CACHE_BYTES)
+#if L1_CACHE_BYTES < 32
+#define NET_SKB_PAD	32
+#else
+#define NET_SKB_PAD	L1_CACHE_BYTES
+#endif
 #endif

 int ___pskb_trim(struct sk_buff *skb, unsigned int len);
--
2.46.0