On 21/01/2026 12:32, Mark Rutland wrote: > On Wed, Jan 21, 2026 at 10:52:21AM +0000, Ryan Roberts wrote: >> On 20/01/2026 23:50, kernel test robot wrote: >>> Hi Ryan, >>> >>> kernel test robot noticed the following build warnings: >>> >>> [auto build test WARNING on akpm-mm/mm-everything] >>> [also build test WARNING on linus/master v6.19-rc6 next-20260119] >>> [cannot apply to tip/sched/core kees/for-next/hardening >>> kees/for-next/execve] >>> [If your patch is applied to the wrong git tree, kindly drop us a note. >>> And when submitting patch, we suggest to use '--base' as documented in >>> https://git-scm.com/docs/git-format-patch#_base_tree_information] >>> >>> url: >>> https://github.com/intel-lab-lkp/linux/commits/Ryan-Roberts/randomize_kstack-Maintain-kstack_offset-per-task/20260119-210329 >>> base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git >>> mm-everything >>> patch link: >>> https://lore.kernel.org/r/20260119130122.1283821-4-ryan.roberts%40arm.com >>> patch subject: [PATCH v4 3/3] randomize_kstack: Unify random source across >>> arches >>> config: x86_64-allmodconfig >>> (https://download.01.org/0day-ci/archive/20260121/[email protected]/config) >>> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project >>> 87f0227cb60147a26a1eeb4fb06e3b505e9c7261) >>> reproduce (this is a W=1 build): >>> (https://download.01.org/0day-ci/archive/20260121/[email protected]/reproduce) >>> >>> If you fix the issue in a separate patch/commit (i.e. not just a new >>> version of >>> the same patch/commit), kindly add following tags >>> | Reported-by: kernel test robot <[email protected]> >>> | Closes: >>> https://lore.kernel.org/oe-kbuild-all/[email protected]/ >>> >>> All warnings (new ones prefixed by >>): >>> >>>>> vmlinux.o: warning: objtool: do_syscall_64+0x2c: call to >>>>> preempt_count_add() leaves .noinstr.text section >>>>> vmlinux.o: warning: objtool: __do_fast_syscall_32+0x3d: call to >>>>> preempt_count_add() leaves .noinstr.text section >> >> Hmm, clearly Dave was correct not to rush this through... yuck. I'll take a >> look, but I guess there is no rush if this won't go into -next until shortly >> after -rc1. > > Sorry, I should have checked the entry sequencing more thoroughly when I > reviewed this,. > > From a quick look, I suspect the right thing to do is to pull the call > to add_random_kstack_offset() a bit later in a few cases; after the > entry logic has run, and after instrumentation_begin() (if the arch code > uses that), such that it doesn't matter if this gets instrumented. > > Considering the callers of add_random_kstack_offset(), if we did that: > > * arm64 is fine as-is. > > * loongarch is fine as-is. > > * powerpc's system_call_exception() would need this moved after the > user_exit_irqoff(). Given that function is notrace rather than > noinstr, it looks like there are bigger extant issues here. > > * riscv is fine as-is. > > * s390's __do_syscall() would need this moved after > enter_from_user_mode(). > > * On x86: > - do_int80_emulation() is fine as-is. > - int80_emulation() is fine as-is. > - do_int80_syscall_32() would need this moved after > instrumentation_begin(). > - __do_fast_syscall_32() would need this moved after > instrumentation_begin(). > - do_syscall_64() would need this moved after instrumentation_begin().
Thanks for the detailed suggestions, Mark. I've taken this approach, and assuming perf testing doesn't throw up any issue, I'm going to revert back to using the out-of-line version of prandom_u32_state() and will drop patch 2. Thanks, Ryan > > Mark.
