On Wed, Sep 1, 2021 at 11:44 AM Greg KH <greg@xxxxxxxxx> wrote: > > On Mon, Aug 30, 2021 at 01:05:56PM +0200, Borislav Petkov wrote: > > > > please queue for 5.10-stable. > > > > See https://bugzilla.kernel.org/show_bug.cgi?id=214159 for more info. > > Now queued up, thanks. I just booted a further of my prod servers with that applied to 5.10.61, patch needed a little mangling, attached below. Once more (as with the 5.4 one), will report about stability in a few days, initially looks fine. best regards Patrick Tested-By: Patrick Schaaf <bof@xxxxxx> diff -purN linux-5.10.61-orig/kernel/kthread.c linux-5.10.61-p/kernel/kthread.c --- linux-5.10.61-orig/kernel/kthread.c 2021-08-26 14:51:21.000000000 +0200 +++ linux-5.10.61-p/kernel/kthread.c 2021-09-01 09:52:31.056738951 +0200 @@ -84,6 +84,25 @@ static inline struct kthread *to_kthread return (__force void *)k->set_child_tid; } +/* + * Variant of to_kthread() that doesn't assume @p is a kthread. + * + * Per construction; when: + * + * (p->flags & PF_KTHREAD) && p->set_child_tid + * + * the task is both a kthread and struct kthread is persistent. However + * PF_KTHREAD on it's own is not, kernel_thread() can exec() (See umh.c and + * begin_new_exec()). + */ +static inline struct kthread *__to_kthread(struct task_struct *p) +{ + void *kthread = (__force void *)p->set_child_tid; + if (kthread && !(p->flags & PF_KTHREAD)) + kthread = NULL; + return kthread; +} + void free_kthread_struct(struct task_struct *k) { struct kthread *kthread; @@ -168,8 +187,9 @@ EXPORT_SYMBOL_GPL(kthread_freezable_shou */ void *kthread_func(struct task_struct *task) { - if (task->flags & PF_KTHREAD) - return to_kthread(task)->threadfn; + struct kthread *kthread = __to_kthread(task); + if (kthread) + return kthread->threadfn; return NULL; } EXPORT_SYMBOL_GPL(kthread_func); @@ -199,10 +219,11 @@ EXPORT_SYMBOL_GPL(kthread_data); */ void *kthread_probe_data(struct task_struct *task) { - struct kthread *kthread = to_kthread(task); + struct kthread *kthread = __to_kthread(task); void *data = NULL; - copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); + if (kthread) + copy_from_kernel_nofault(&data, &kthread->data, sizeof(data)); return data; } @@ -514,9 +535,9 @@ void kthread_set_per_cpu(struct task_str set_bit(KTHREAD_IS_PER_CPU, &kthread->flags); } -bool kthread_is_per_cpu(struct task_struct *k) +bool kthread_is_per_cpu(struct task_struct *p) { - struct kthread *kthread = to_kthread(k); + struct kthread *kthread = __to_kthread(p); if (!kthread) return false; diff -purN linux-5.10.61-orig/kernel/sched/fair.c linux-5.10.61-p/kernel/sched/fair.c --- linux-5.10.61-orig/kernel/sched/fair.c 2021-08-26 14:51:21.000000000 +0200 +++ linux-5.10.61-p/kernel/sched/fair.c 2021-09-01 09:48:06.860333848 +0200 @@ -7569,7 +7569,7 @@ int can_migrate_task(struct task_struct return 0; /* Disregard pcpu kthreads; they are where they need to be. */ - if ((p->flags & PF_KTHREAD) && kthread_is_per_cpu(p)) + if (kthread_is_per_cpu(p)) return 0; if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) {
