On Wed, May 19, 2021 at 09:02:34AM -0000, tip-bot2 for Yejune Deng wrote: > The following commit has been merged into the sched/core branch of tip: > > Commit-ID: 570a752b7a9bd03b50ad6420cd7f10092cc11bd3 > Gitweb: https://git.kernel.org/tip/570a752b7a9bd03b50ad6420cd7f10092cc11bd3 > Author: Yejune Deng <yejune.deng@xxxxxxxxx> > AuthorDate: Mon, 10 May 2021 16:10:24 +01:00 > Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > CommitterDate: Wed, 19 May 2021 10:51:40 +02:00 > > lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed > > is_percpu_thread() more elegantly handles SMP vs UP, and further checks the > presence of PF_NO_SETAFFINITY. This lets us catch cases where > check_preemption_disabled() can race with a concurrent sched_setaffinity(). > > Signed-off-by: Yejune Deng <yejune.deng@xxxxxxxxx> > [Amended changelog] > Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@xxxxxxx > --- > lib/smp_processor_id.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c > index 1c1dbd3..046ac62 100644 > --- a/lib/smp_processor_id.c > +++ b/lib/smp_processor_id.c > @@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2) > if (irqs_disabled()) > goto out; > > - /* > - * Kernel threads bound to a single CPU can safely use > - * smp_processor_id(): > - */ > - if (current->nr_cpus_allowed == 1) > + if (is_percpu_thread()) > goto out; So my test box was unhappy with all this and started spewing lots of DEBUG_PREEMPT warns on boot. This extends 8fb12156b8db6 to cover the new requirement. --- Subject: sched,init: Fix DEBUG_PREEMPT vs early boot Extend 8fb12156b8db ("init: Pin init task to the boot CPU, initially") to cover the new PF_NO_SETAFFINITY requirement. While there, move wait_for_completion(&kthreadd_done) into kernel_init() to make it absolutely clear it is the very first thing done by the init thread. Fixes: 570a752b7a9b ("lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed") Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> --- init/main.c | 11 ++++++----- kernel/sched/core.c | 1 + 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/init/main.c b/init/main.c index 7b027d9c5c89..e945ec82b8a5 100644 --- a/init/main.c +++ b/init/main.c @@ -692,6 +692,7 @@ noinline void __ref rest_init(void) */ rcu_read_lock(); tsk = find_task_by_pid_ns(pid, &init_pid_ns); + tsk->flags |= PF_NO_SETAFFINITY; set_cpus_allowed_ptr(tsk, cpumask_of(smp_processor_id())); rcu_read_unlock(); @@ -1440,6 +1441,11 @@ static int __ref kernel_init(void *unused) { int ret; + /* + * Wait until kthreadd is all set-up. + */ + wait_for_completion(&kthreadd_done); + kernel_init_freeable(); /* need to finish all async __init code before freeing the memory */ async_synchronize_full(); @@ -1520,11 +1526,6 @@ void __init console_on_rootfs(void) static noinline void __init kernel_init_freeable(void) { - /* - * Wait until kthreadd is all set-up. - */ - wait_for_completion(&kthreadd_done); - /* Now the scheduler is fully set up and can do blocking allocations */ gfp_allowed_mask = __GFP_BITS_MASK; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index adea0b1e8036..ae7737e6c2b2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8867,6 +8867,7 @@ void __init sched_init_smp(void) /* Move init over to a non-isolated CPU */ if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0) BUG(); + current->flags &= ~PF_NO_SETAFFINITY; sched_init_granularity(); init_sched_rt_class();
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