kthread: Extract KTHREAD_IS_PER_CPU

xiaomi-sm8450/android_kernel_xiaomi_sm8450

[ 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>

This commit is contained in:

Peter Zijlstra

2021-01-12 11:24:04 +01:00

committed by

Greg Kroah-Hartman

parent d8649eb8e3

commit b20475a80b

3 changed files with 30 additions and 1 deletions

									
										1

kernel/smpboot.c
									
												View File
												
				@@ -188,6 +188,7 @@ __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)

						kfree(td);

						return PTR_ERR(tsk);

					}

					kthread_set_per_cpu(tsk, cpu);

					/*

					 * Park the thread so that it could start right on the CPU

					 * when it is available.

kthread: Extract KTHREAD_IS_PER_CPU

1 kernel/smpboot.c Unescape Escape View File

1

kernel/smpboot.c

View File