On Fri, Feb 27, 2015 at 03:29:38PM -0500, Pranith Kumar wrote: > On Fri, Feb 27, 2015 at 3:17 PM, Pranith Kumar <[email protected]> wrote: > > On Fri, Feb 27, 2015 at 3:15 PM, Will Deacon <[email protected]> wrote: > >>> @@ -166,11 +166,11 @@ static inline int __cmpxchg_double(volatile void > >>> *ptr1, volatile void *ptr2, > >>> VM_BUG_ON((unsigned long *)ptr2 - (unsigned long *)ptr1 != > >>> 1); > >>> do { > >>> asm volatile("// __cmpxchg_double8\n" > >>> + " mov %w0, #0\n" > >>> " ldxp %0, %1, %2\n" > >> > >> Seriously, you might want to test this before you mindlessly make changes > >> to > >> low-level synchronisation code. Not only is the change completely > >> unnecessary > >> but it is actively harmful. > >> > > > > Oops, I apologize for this. I should have looked more closely. It is > > wrong to do this in cmpxchg_double(). What about the other cases? > > I tried looking closely on what might be the problem here. I am > waiting on a HiKey arm64 board and I agree I should not send in > changes without running/testing them first. > > Could you please explain (for educational purposes) why you think this > change is harmful?
Do you mean the cmpxchg_double() change? Becuase %w0 and %0 is the same physical register. You set it to 0 and immediately override it with ldxp. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
