On Wed 2023-07-19 22:15:38, Peter Zijlstra wrote: > On Wed, Jul 19, 2023 at 10:02:22PM +0200, Peter Zijlstra wrote: > > On Wed, Jul 19, 2023 at 05:21:11PM +0200, Petr Mladek wrote: > > > > > This patch broke livepatching. Kthreads never have a reliable stack. > > > It works when I revert it. > > > > > > +SYM_CODE_START(ret_from_fork_asm) > > > > + UNWIND_HINT_REGS > > > > It works again when I change the above hint to UNWIND_HINT_END_OF_STACK, > > so yeah. Doing this makes objtool unhappy with something else though, > > so I'll go prod at things with something sharp... > > > The below cures things; Josh, did I miss anything? I can confirm that it solved the problem. Feel free to use: Tested-by: Petr Mladek <pmladek@xxxxxxxx> Thanks a lot for the quick fix. Best Regards, Petr > --- > arch/x86/entry/entry_64.S | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index 91f6818884fa..cfe7882ea9ae 100644 > --- a/arch/x86/entry/entry_64.S > +++ b/arch/x86/entry/entry_64.S > @@ -285,7 +285,14 @@ SYM_FUNC_END(__switch_to_asm) > */ > .pushsection .text, "ax" > SYM_CODE_START(ret_from_fork_asm) > - UNWIND_HINT_REGS > + /* > + * This is the start of the kernel stack; even through there's a regs > + * set at the top, there is no real exception frame and one cannot > + * unwind further. This is the end. > + * > + * This ensures stack unwinds of kernel threads hit a known good state. > + */ > + UNWIND_HINT_END_OF_STACK > ANNOTATE_NOENDBR // copy_thread > CALL_DEPTH_ACCOUNT > > @@ -295,6 +302,11 @@ SYM_CODE_START(ret_from_fork_asm) > movq %r12, %rcx /* fn_arg */ > call ret_from_fork > > + /* > + * Set the stack state to what is expected for the target function > + * -- also it is not wrong. > + */ > + UNWIND_HINT_REGS > jmp swapgs_restore_regs_and_return_to_usermode > SYM_CODE_END(ret_from_fork_asm) > .popsection
