Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Date | Wed, 18 Oct 2023 11:04:30 +0200 | Subject | Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr() |
| |
On Wed, Oct 18, 2023 at 9:46 AM Uros Bizjak <ubizjak@gmail.com> wrote: > > On Tue, Oct 17, 2023 at 11:53 PM Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > On Tue, 17 Oct 2023 at 14:06, Uros Bizjak <ubizjak@gmail.com> wrote: > > > > > > But adding the attached patch on top of both patches boots OK. > > > > Funky. > > > > Mind adding a > > > > WARN_ON_ONCE(!active_mm); > > > > to there to give a nice backtrace for the odd NULL case. > > [ 4.907840] Call Trace: > [ 4.908909] <TASK> > [ 4.909858] ? __warn+0x7b/0x120 > [ 4.911108] ? begin_new_exec+0x90f/0xa30 > [ 4.912602] ? report_bug+0x164/0x190 > [ 4.913929] ? handle_bug+0x3c/0x70 > [ 4.915179] ? exc_invalid_op+0x17/0x70 > [ 4.916569] ? asm_exc_invalid_op+0x1a/0x20 > [ 4.917969] ? begin_new_exec+0x90f/0xa30 > [ 4.919303] ? begin_new_exec+0x3ce/0xa30 > [ 4.920667] ? load_elf_phdrs+0x67/0xb0 > [ 4.921935] load_elf_binary+0x2bb/0x1770 > [ 4.923262] ? __kernel_read+0x136/0x2d0 > [ 4.924563] bprm_execve+0x277/0x630 > [ 4.925703] kernel_execve+0x145/0x1a0 > [ 4.926890] call_usermodehelper_exec_async+0xcb/0x180 > [ 4.928408] ? __pfx_call_usermodehelper_exec_async+0x10/0x10 > [ 4.930515] ret_from_fork+0x2f/0x50 > [ 4.931894] ? __pfx_call_usermodehelper_exec_async+0x10/0x10 > [ 4.933941] ret_from_fork_asm+0x1b/0x30 > [ 4.935371] </TASK> > [ 4.936212] ---[ end trace 0000000000000000 ]--- > > > > > That code *is* related to 'current', in how we do > > > > tsk = current; > > ... > > local_irq_disable(); > > active_mm = tsk->active_mm; > > tsk->active_mm = mm; > > tsk->mm = mm; > > ... > > activate_mm(active_mm, mm); > > ... > > mmdrop_lazy_tlb(active_mm); > > > > but I don't see how 'active_mm' could *poossibly* be validly NULL > > here, and why caching 'current' would matter and change it. > > I have also added "__attribute__((optimize(0)))" to exec_mmap() to > weed out compiler bugs. The result was the same oops in > mmdrop_lazy_tlb. > > Also, when using WARN_ON instead of WARN_ON_ONCE, it triggers only > once during the whole boot, with the above trace. > > Another observation: adding WARN_ON to the top of exec_mmap: > > WARN_ON(!current->active_mm); > /* Notify parent that we're no longer interested in the old VM */ > tsk = current; > old_mm = current->mm; > > also triggers WARN, suggesting that current does not have active_mm > set on the entry to the function.
Solved.
All that is needed is to patch cpu_init() from arch/x86/kernel/cpu/common.c with:
--cut here-- diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index b14fc8c1c953..61b6fcdf6937 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -2228,7 +2232,7 @@ void cpu_init_exception_handling(void) */ void cpu_init(void) { - struct task_struct *cur = current; + struct task_struct *cur = this_cpu_read_stable(pcpu_hot.current_task); int cpu = raw_smp_processor_id();
#ifdef CONFIG_NUMA --cut here--
This is effectively the old get_current(). Since we declare and export
+DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override, + const_pcpu_hot) __attribute__((alias("pcpu_hot"))); +EXPORT_PER_CPU_SYMBOL(const_pcpu_hot); in the same file, and the "new" current represents just
return const_pcpu_hot.current_task;
GCC assumes and over-optimizes something and seemingly doesn't fully initialize the
cur->active_mm = &init_mm;
below.
Have to run now, but this will be easy to fix.
Uros.
| |