From: "tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
Valentin Schneider <valentin.schneider@arm.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: sched/urgent] kthread: Extract KTHREAD_IS_PER_CPU
Date: Fri, 22 Jan 2021 17:41:35 -0000 [thread overview]
Message-ID: <161133729574.414.5257210132156669609.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210121103506.557620262@infradead.org>
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: ac687e6e8c26181a33270efd1a2e2241377924b0
Gitweb: https://git.kernel.org/tip/ac687e6e8c26181a33270efd1a2e2241377924b0
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 12 Jan 2021 11:24:04 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 22 Jan 2021 15:09:42 +01:00
kthread: Extract KTHREAD_IS_PER_CPU
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
---
include/linux/kthread.h | 3 +++
kernel/kthread.c | 27 ++++++++++++++++++++++++++-
kernel/smpboot.c | 1 +
3 files changed, 30 insertions(+), 1 deletion(-)
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 65b81e0..2484ed9 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -33,6 +33,9 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
unsigned int cpu,
const char *namefmt);
+void kthread_set_per_cpu(struct task_struct *k, int cpu);
+bool kthread_is_per_cpu(struct task_struct *k);
+
/**
* kthread_run - create and wake a thread.
* @threadfn: the function to run until signal_pending(current).
diff --git a/kernel/kthread.c b/kernel/kthread.c
index a5eceec..e0e4a42 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -493,11 +493,36 @@ 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().
diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 2efe1e2..f25208e 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -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.
next prev parent reply other threads:[~2021-01-22 17:56 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 10:17 [PATCH -v3 0/9] sched: Fix hot-unplug regression Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 1/9] sched/core: Print out straggler tasks in sched_cpu_dying() Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 2/9] workqueue: Use cpu_possible_mask instead of cpu_active_mask to break affinity Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 3/9] sched: Dont run cpu-online with balance_push() enabled Peter Zijlstra
2021-01-21 14:00 ` Valentin Schneider
2021-01-21 14:14 ` Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] sched: Don't " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 4/9] kthread: Extract KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-22 17:41 ` tip-bot2 for Peter Zijlstra [this message]
2021-01-21 10:17 ` [PATCH -v3 5/9] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-21 14:31 ` Valentin Schneider
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 6/9] workqueue: Restrict affinity change to rescuer Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 7/9] sched: Prepare to use balance_push in ttwu() Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 8/9] sched: Fix CPU hotplug / tighten is_per_cpu_kthread() Peter Zijlstra
2021-01-21 14:01 ` Valentin Schneider
2021-01-21 14:18 ` Peter Zijlstra
2021-01-21 14:36 ` Valentin Schneider
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 9/9] sched: Relax the set_cpus_allowed_ptr() semantics Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 14:36 ` [PATCH -v3 0/9] sched: Fix hot-unplug regression Valentin Schneider
2021-01-21 19:56 ` Paul E. McKenney
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