Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 13 Mar 2018 11:49:17 +0300 | Subject | Re: [tip:locking/core 9/11] include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates bits from constant value (100 becomes 0) |
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On Mon, Mar 12, 2018 at 6:17 PM, Dmitry Vyukov <dvyukov@google.com> wrote: > On Mon, Mar 12, 2018 at 5:52 PM, kbuild test robot > <fengguang.wu@intel.com> wrote: >> tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking/core >> head: ac605bee0bfab40fd5d11964705e907d2d5a32de >> commit: 8bf705d130396e69c04cd8e6e010244ad2ce71f4 [9/11] locking/atomic/x86: Switch atomic.h to use atomic-instrumented.h >> reproduce: >> # apt-get install sparse >> git checkout 8bf705d130396e69c04cd8e6e010244ad2ce71f4 >> make ARCH=x86_64 allmodconfig >> make C=1 CF=-D__CHECK_ENDIAN__ >> >> >> sparse warnings: (new ones prefixed by >>) >> >> kernel/locking/qspinlock.c:418:22: sparse: incorrect type in assignment (different modifiers) @@ expected struct mcs_spinlock *prev @@ got struct struct mcs_spinlock *prev @@ >> kernel/locking/qspinlock.c:418:22: expected struct mcs_spinlock *prev >> kernel/locking/qspinlock.c:418:22: got struct mcs_spinlock [pure] * >> kernel/locking/qspinlock_paravirt.h:519:1: sparse: symbol '__pv_queued_spin_unlock_slowpath' was not declared. Should it be static? >> kernel/locking/qspinlock.c:418:22: sparse: incorrect type in assignment (different modifiers) @@ expected struct mcs_spinlock *prev @@ got struct struct mcs_spinlock *prev @@ >> kernel/locking/qspinlock.c:418:22: expected struct mcs_spinlock *prev >> kernel/locking/qspinlock.c:418:22: got struct mcs_spinlock [pure] * >>>> include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates bits from constant value (100 becomes 0) >> >> vim +288 include/asm-generic/atomic-instrumented.h >> >> b06ed71a6 Dmitry Vyukov 2018-01-29 282 >> b06ed71a6 Dmitry Vyukov 2018-01-29 283 static __always_inline unsigned long >> b06ed71a6 Dmitry Vyukov 2018-01-29 284 cmpxchg_size(volatile void *ptr, unsigned long old, unsigned long new, int size) >> b06ed71a6 Dmitry Vyukov 2018-01-29 285 { >> b06ed71a6 Dmitry Vyukov 2018-01-29 286 switch (size) { >> b06ed71a6 Dmitry Vyukov 2018-01-29 287 case 1: >> b06ed71a6 Dmitry Vyukov 2018-01-29 @288 return arch_cmpxchg((u8 *)ptr, (u8)old, (u8)new); >> b06ed71a6 Dmitry Vyukov 2018-01-29 289 case 2: >> b06ed71a6 Dmitry Vyukov 2018-01-29 290 return arch_cmpxchg((u16 *)ptr, (u16)old, (u16)new); >> b06ed71a6 Dmitry Vyukov 2018-01-29 291 case 4: >> b06ed71a6 Dmitry Vyukov 2018-01-29 292 return arch_cmpxchg((u32 *)ptr, (u32)old, (u32)new); >> b06ed71a6 Dmitry Vyukov 2018-01-29 293 case 8: >> b06ed71a6 Dmitry Vyukov 2018-01-29 294 BUILD_BUG_ON(sizeof(unsigned long) != 8); >> b06ed71a6 Dmitry Vyukov 2018-01-29 295 return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new); >> b06ed71a6 Dmitry Vyukov 2018-01-29 296 } >> b06ed71a6 Dmitry Vyukov 2018-01-29 297 BUILD_BUG(); >> b06ed71a6 Dmitry Vyukov 2018-01-29 298 return 0; >> b06ed71a6 Dmitry Vyukov 2018-01-29 299 } >> b06ed71a6 Dmitry Vyukov 2018-01-29 300 >> >> :::::: The code at line 288 was first introduced by commit >> :::::: b06ed71a624ba088a3e3e3ac7d4185f48c7c1660 locking/atomic, asm-generic: Add asm-generic/atomic-instrumented.h >> >> :::::: TO: Dmitry Vyukov <dvyukov@google.com> >> :::::: CC: Ingo Molnar <mingo@kernel.org> > > > I will take a look tomorrow.
It seems that this is due to this guy:
static __always_inline int trylock_clear_pending(struct qspinlock *lock) { struct __qspinlock *l = (void *)lock;
return !READ_ONCE(l->locked) && (cmpxchg_acquire(&l->locked_pending, _Q_PENDING_VAL, _Q_LOCKED_VAL) == _Q_PENDING_VAL); }
_Q_PENDING_VAL is 0x100. However, locked_pending is 2 bytes. So it seems that compiler checks all switch cases, this inevitably will lead to such warnings.
Any suggestion on how to resolve this? Leave as is?
Off the top of my head I can think of the following solution:
switch (size) { case 1: return arch_cmpxchg((u8 *)ptr, (u8)(old * (size != 1)), (u8)(new * (size != 1))); case 2: return arch_cmpxchg((u16 *)ptr, (u16)(old * (size != 2)), (u16)(new * (size != 2)));
But it's too ugly.
FTR, the following was helpful to find invocations with particular size:
#define cmpxchg(ptr, old, new) \ ({ \ + BUILD_BUG_ON(sizeof(*(ptr)) == 1); \ ((__typeof__(*(ptr)))cmpxchg_size((ptr), (unsigned long)(old), \ (unsigned long)(new), sizeof(*(ptr)))); \ })
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