linux-kernel - arch/powerpc/include/asm/cmpxchg.h:241:47: sparse: sparse: cast truncates bits from constant value (8000000000000000 becomes 0)

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Date: Sat, 17 Feb 2024 02:24:41 +0800
From: kernel test robot <lkp@...el.com>
To: David Howells <dhowells@...hat.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: arch/powerpc/include/asm/cmpxchg.h:241:47: sparse: sparse: cast
 truncates bits from constant value (8000000000000000 becomes 0)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   0f1dd5e91e2ba3990143645faff2bcce2d99778e
commit: 453924de6212ac159f946b75c6b59918e2e30944 afs: Overhaul invalidation handling to better support RO volumes
date:   7 weeks ago
config: powerpc64-randconfig-r111-20240216 (https://download.01.org/0day-ci/archive/20240217/202402170208.0xYZculA-lkp@intel.com/config)
compiler: powerpc64-linux-gcc (GCC) 13.2.0
reproduce: (https://download.01.org/0day-ci/archive/20240217/202402170208.0xYZculA-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202402170208.0xYZculA-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
   fs/afs/callback.c: note: in included file (through arch/powerpc/include/asm/pgtable-be-types.h, arch/powerpc/include/asm/page.h, arch/powerpc/include/asm/mmu.h, ...):
>> arch/powerpc/include/asm/cmpxchg.h:241:47: sparse: sparse: cast truncates bits from constant value (8000000000000000 becomes 0)
   arch/powerpc/include/asm/cmpxchg.h:243:48: sparse: sparse: cast truncates bits from constant value (8000000000000000 becomes 0)
   fs/afs/callback.c:146:22: sparse: sparse: context imbalance in 'afs_lookup_volume_rcu' - different lock contexts for basic block
--
   fs/afs/rotate.c: note: in included file (through arch/powerpc/include/asm/pgtable-be-types.h, arch/powerpc/include/asm/page.h, arch/powerpc/include/asm/mmu.h, ...):
>> arch/powerpc/include/asm/cmpxchg.h:241:47: sparse: sparse: cast truncates bits from constant value (8000000000000000 becomes 0)
   arch/powerpc/include/asm/cmpxchg.h:243:48: sparse: sparse: cast truncates bits from constant value (8000000000000000 becomes 0)
   fs/afs/rotate.c:655:42: sparse: sparse: self-comparison always evaluates to true

vim +241 arch/powerpc/include/asm/cmpxchg.h

ae3a197e3d0bfe David Howells 2012-03-28  235  
ae3a197e3d0bfe David Howells 2012-03-28  236  static __always_inline unsigned long
26760fc19a7e66 Boqun Feng    2015-12-15  237  __xchg_relaxed(void *ptr, unsigned long x, unsigned int size)
ae3a197e3d0bfe David Howells 2012-03-28  238  {
ae3a197e3d0bfe David Howells 2012-03-28  239  	switch (size) {
d0563a1297e234 Pan Xinhui    2016-04-27  240  	case 1:
d0563a1297e234 Pan Xinhui    2016-04-27 @241  		return __xchg_u8_relaxed(ptr, x);
d0563a1297e234 Pan Xinhui    2016-04-27  242  	case 2:
d0563a1297e234 Pan Xinhui    2016-04-27  243  		return __xchg_u16_relaxed(ptr, x);
ae3a197e3d0bfe David Howells 2012-03-28  244  	case 4:
26760fc19a7e66 Boqun Feng    2015-12-15  245  		return __xchg_u32_relaxed(ptr, x);
ae3a197e3d0bfe David Howells 2012-03-28  246  #ifdef CONFIG_PPC64
ae3a197e3d0bfe David Howells 2012-03-28  247  	case 8:
26760fc19a7e66 Boqun Feng    2015-12-15  248  		return __xchg_u64_relaxed(ptr, x);
ae3a197e3d0bfe David Howells 2012-03-28  249  #endif
ae3a197e3d0bfe David Howells 2012-03-28  250  	}
068550631fbe0b Andrzej Hajda 2023-01-18  251  	BUILD_BUG_ON_MSG(1, "Unsupported size for __xchg_relaxed");
ae3a197e3d0bfe David Howells 2012-03-28  252  	return x;
ae3a197e3d0bfe David Howells 2012-03-28  253  }
9eaa82935dccb7 Mark Rutland  2021-05-25  254  #define arch_xchg_local(ptr,x)						     \
ae3a197e3d0bfe David Howells 2012-03-28  255    ({									     \
ae3a197e3d0bfe David Howells 2012-03-28  256       __typeof__(*(ptr)) _x_ = (x);					     \
26760fc19a7e66 Boqun Feng    2015-12-15  257       (__typeof__(*(ptr))) __xchg_local((ptr),				     \
26760fc19a7e66 Boqun Feng    2015-12-15  258       		(unsigned long)_x_, sizeof(*(ptr))); 			     \
ae3a197e3d0bfe David Howells 2012-03-28  259    })
ae3a197e3d0bfe David Howells 2012-03-28  260  

:::::: The code at line 241 was first introduced by commit
:::::: d0563a1297e234ed37f6b51c2e9321accebd1839 powerpc: Implement {cmp}xchg for u8 and u16

:::::: TO: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
:::::: CC: Michael Ellerman <mpe@...erman.id.au>

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