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authorPeter Zijlstra <peterz@infradead.org>2021-01-12 11:24:04 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-02-07 14:48:38 +0100
commitfbad32181af9c8c76698b16115c28a493c26a2ee (patch)
treebb1f57e3a5d1c48169a7b235c1d9a3c42bdc2067 /kernel/kthread.c
parent52b4c58bac0e03732961d6d1c29c21a1eb7364e5 (diff)
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kthread: Extract KTHREAD_IS_PER_CPU
[ Upstream commit ac687e6e8c26181a33270efd1a2e2241377924b0 ] There is a need to distinguish geniune per-cpu kthreads from kthreads that happen to have a single CPU affinity. Geniune per-cpu kthreads are kthreads that are CPU affine for correctness, these will obviously have PF_KTHREAD set, but must also have PF_NO_SETAFFINITY set, lest userspace modify their affinity and ruins things. However, these two things are not sufficient, PF_NO_SETAFFINITY is also set on other tasks that have their affinities controlled through other means, like for instance workqueues. Therefore another bit is needed; it turns out kthread_create_per_cpu() already has such a bit: KTHREAD_IS_PER_CPU, which is used to make kthread_park()/kthread_unpark() work correctly. Expose this flag and remove the implicit setting of it from kthread_create_on_cpu(); the io_uring usage of it seems dubious at best. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Tested-by: Valentin Schneider <valentin.schneider@arm.com> Link: https://lkml.kernel.org/r/20210121103506.557620262@infradead.org Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel/kthread.c')
-rw-r--r--kernel/kthread.c27
1 files changed, 26 insertions, 1 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 2eed853ab9cc..81abfac35127 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -460,11 +460,36 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
return p;
kthread_bind(p, cpu);
/* CPU hotplug need to bind once again when unparking the thread. */
- set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
to_kthread(p)->cpu = cpu;
return p;
}
+void kthread_set_per_cpu(struct task_struct *k, int cpu)
+{
+ struct kthread *kthread = to_kthread(k);
+ if (!kthread)
+ return;
+
+ WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
+
+ if (cpu < 0) {
+ clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+ return;
+ }
+
+ kthread->cpu = cpu;
+ set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+}
+
+bool kthread_is_per_cpu(struct task_struct *k)
+{
+ struct kthread *kthread = to_kthread(k);
+ if (!kthread)
+ return false;
+
+ return test_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
+}
+
/**
* kthread_unpark - unpark a thread created by kthread_create().
* @k: thread created by kthread_create().