On Sat, Aug 22, 2020 at 02:08:27PM -0700, Linus Torvalds wrote: > However, in this case, can we just leave that old "__force_order" hack > alone, and to work around the clang thing, just make a dummy > definition of it anyway. > > Alternatively, just use the memory clobber. We use memory clobbers > elsewhere in inline asms to make sure they are serialized, it's not > normally a huge problem. Both clang and gcc should be smart enough to > know that a memory clobber doesn't matter for things like local > variables etc that might be on stack but have never had their address > taken. > > Or are there other cases than that particular __force_order thing that > people now worry about? > > Linus
Actually, is a memory clobber required for correctness? Memory accesses probably shouldn't be reordered across a CRn write. Is asm volatile enough to stop that or do you need a memory clobber? Replacing force_order with memory clobber introduces a few extra instructions (testing with defconfig), but only in x86-64 hibernate/reboot/sleep code and early_ioremap_init on x86-32.
