From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 229E0C7EE33 for ; Thu, 2 Mar 2023 09:00:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229824AbjCBJAp (ORCPT ); Thu, 2 Mar 2023 04:00:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229750AbjCBJAm (ORCPT ); Thu, 2 Mar 2023 04:00:42 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86A9A392BC; Thu, 2 Mar 2023 01:00:40 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 3DF22B811A1; Thu, 2 Mar 2023 09:00:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3020DC433D2; Thu, 2 Mar 2023 09:00:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1677747638; bh=Ebb3ot/MKrEX9PZqTOLwhhuImbtXpjRuOQVB90BniQY=; h=From:To:Cc:Subject:Date:From; b=cpzf7ma+ctc+LuCj9wJ7uRvZWsBa/ogBWcU5vYxz+PUs1CmIJ2euxkIoy+twdxpxM Ed6rzepfq8FUOAHgkagE3ojujl0E1MWtifIWCTxKXKKLi1sFFrkhMnBeH5iQUoOOIt MFUSpEPXruw1IEE+h/EpiGHOCFvQ/mrWCJORjGRIA5o4MH5yYv7KHnHPU2LKyKKPpf jjzwu6/IJiVnxj/s3GqKTTiypI6o/MK9duqV7aOIDkkJryupHzjk4eGX3F7YmCRnWY zbIyv7+WLvsfPatfvzqHDJC1eqPVMqu2pGmLWnwy54EeJt2Mr3pna9i0kXwYcfhuHw +WfWCq4yQu/QA== From: Arnd Bergmann To: Will Deacon , Peter Zijlstra , Arnd Bergmann , Matt Evans Cc: Boqun Feng , Mark Rutland , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Subject: [PATCH] asm-generic: avoid __generic_cmpxchg_local warnings Date: Thu, 2 Mar 2023 10:00:22 +0100 Message-Id: <20230302090032.3740505-1-arnd@kernel.org> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arnd Bergmann Code that passes a 32-bit constant into cmpxchg() produces a harmless sparse warning because of the truncation in the branch that is not taken: fs/erofs/zdata.c: note: in included file (through /home/arnd/arm-soc/arch/arm/include/asm/cmpxchg.h, /home/arnd/arm-soc/arch/arm/include/asm/atomic.h, /home/arnd/arm-soc/include/linux/atomic.h, ...): include/asm-generic/cmpxchg-local.h:29:33: warning: cast truncates bits from constant value (5f0ecafe becomes fe) include/asm-generic/cmpxchg-local.h:33:34: warning: cast truncates bits from constant value (5f0ecafe becomes cafe) include/asm-generic/cmpxchg-local.h:29:33: warning: cast truncates bits from constant value (5f0ecafe becomes fe) include/asm-generic/cmpxchg-local.h:30:42: warning: cast truncates bits from constant value (5f0edead becomes ad) include/asm-generic/cmpxchg-local.h:33:34: warning: cast truncates bits from constant value (5f0ecafe becomes cafe) include/asm-generic/cmpxchg-local.h:34:44: warning: cast truncates bits from constant value (5f0edead becomes dead) This was reported as a regression to Matt's recent __generic_cmpxchg_local patch, though this patch only added more warnings on top of the ones that were already there. Rewording the truncation to use an explicit bitmask instead of a cast to a smaller type avoids the warning but otherwise leaves the code unchanged. I had another look at why the cast is even needed for atomic_cmpxchg(), and as Matt describes the problem here is that atomic_t contains a signed 'int', but cmpxchg() takes an 'unsigned long' argument, and converting between the two leads to a 64-bit sign-extension of negative 32-bit atomics. I checked the other implementations of arch_cmpxchg() and did not find any others that run into the same problem as __generic_cmpxchg_local(), but it's easy to be on the safe side here and always convert the signed int into an unsigned int when calling arch_cmpxchg(), as this will work even when any of the arch_cmpxchg() implementations run into the same problem. Fixes: 624654152284 ("locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare against zero-extended 'old' value") Reviewed-by: Matt Evans Signed-off-by: Arnd Bergmann --- include/asm-generic/atomic.h | 4 ++-- include/asm-generic/cmpxchg-local.h | 12 ++++++------ include/asm-generic/cmpxchg.h | 6 +++--- 3 files changed, 11 insertions(+), 11 deletions(-) diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h index 04b8be9f1a77..e271d6708c87 100644 --- a/include/asm-generic/atomic.h +++ b/include/asm-generic/atomic.h @@ -130,7 +130,7 @@ ATOMIC_OP(xor, ^) #define arch_atomic_read(v) READ_ONCE((v)->counter) #define arch_atomic_set(v, i) WRITE_ONCE(((v)->counter), (i)) -#define arch_atomic_xchg(ptr, v) (arch_xchg(&(ptr)->counter, (v))) -#define arch_atomic_cmpxchg(v, old, new) (arch_cmpxchg(&((v)->counter), (old), (new))) +#define arch_atomic_xchg(ptr, v) (arch_xchg(&(ptr)->counter, (u32)(v))) +#define arch_atomic_cmpxchg(v, old, new) (arch_cmpxchg(&((v)->counter), (u32)(old), (u32)(new))) #endif /* __ASM_GENERIC_ATOMIC_H */ diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h index c3e7315b7c1d..3df9f59a544e 100644 --- a/include/asm-generic/cmpxchg-local.h +++ b/include/asm-generic/cmpxchg-local.h @@ -26,16 +26,16 @@ static inline unsigned long __generic_cmpxchg_local(volatile void *ptr, raw_local_irq_save(flags); switch (size) { case 1: prev = *(u8 *)ptr; - if (prev == (u8)old) - *(u8 *)ptr = (u8)new; + if (prev == (old & 0xffu)) + *(u8 *)ptr = (new & 0xffu); break; case 2: prev = *(u16 *)ptr; - if (prev == (u16)old) - *(u16 *)ptr = (u16)new; + if (prev == (old & 0xffffu)) + *(u16 *)ptr = (new & 0xffffu); break; case 4: prev = *(u32 *)ptr; - if (prev == (u32)old) - *(u32 *)ptr = (u32)new; + if (prev == (old & 0xffffffffffu)) + *(u32 *)ptr = (new & 0xffffffffu); break; case 8: prev = *(u64 *)ptr; if (prev == old) diff --git a/include/asm-generic/cmpxchg.h b/include/asm-generic/cmpxchg.h index dca4419922a9..848de25fc4bf 100644 --- a/include/asm-generic/cmpxchg.h +++ b/include/asm-generic/cmpxchg.h @@ -32,7 +32,7 @@ unsigned long __generic_xchg(unsigned long x, volatile void *ptr, int size) #else local_irq_save(flags); ret = *(volatile u8 *)ptr; - *(volatile u8 *)ptr = x; + *(volatile u8 *)ptr = (x & 0xffu); local_irq_restore(flags); return ret; #endif /* __xchg_u8 */ @@ -43,7 +43,7 @@ unsigned long __generic_xchg(unsigned long x, volatile void *ptr, int size) #else local_irq_save(flags); ret = *(volatile u16 *)ptr; - *(volatile u16 *)ptr = x; + *(volatile u16 *)ptr = (x & 0xffffu); local_irq_restore(flags); return ret; #endif /* __xchg_u16 */ @@ -54,7 +54,7 @@ unsigned long __generic_xchg(unsigned long x, volatile void *ptr, int size) #else local_irq_save(flags); ret = *(volatile u32 *)ptr; - *(volatile u32 *)ptr = x; + *(volatile u32 *)ptr = (x & 0xffffffffu); local_irq_restore(flags); return ret; #endif /* __xchg_u32 */ -- 2.39.2