On Wed, Feb 25, 2015 at 1:45 AM, Ingo Molnar <mi...@kernel.org> wrote: > > * Andy Lutomirski <l...@amacapital.net> wrote: > >> - BUG_ON(((current_stack_pointer() ^ >> this_cpu_read_stable(kernel_stack)) >> + BUG_ON(((current_stack_pointer() ^ >> + (this_cpu_read_stable(kernel_stack) - 1)) >> & ~(THREAD_SIZE - 1)) != 0); >> >> preempt_count_sub(HARDIRQ_OFFSET); >> >> I added that in and applied this patch. > > So this is not just slightly buggy, it's fundamentally > wrong as well as it removes the possibility of an RSP value > optimization from the 64-bit path, see my previous mail.
This is just trying to check that the function is executing on the per-thread stack. It was correct (and fairly heavily tested by Tony) wither KERNEL_STACK_OFFSET being nonzero, but we're checking the wrong page if KERNEL_STACK_OFFSET becomes zero. I don't think I understand your objection to this bit. > > The right solution would be to make SAVE_ARGS recognize > when KERNEL_STACK_OFFSET == args-offset and omit the RSP > fixup in that case, or to simply use a __SAVE_ARGS for the > 64-bit path, knowing that RSP has the right value already. > > Please also add comments that explain the relationship > between percpu::kernel_stack, KERNEL_STACK_OFFSET and the > 64-bit system call entry code. > > Also, guys, please slow down a bit and be more careful. > Andy, could you please send me all currently pending entry > bits pending in your tree, because all the in-flight > changes make it hard for me to review patches? Please > (re-)send all patches as well as part of the submission. Will do later today. Note that someone just found a bug as a result of this being in -next. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
