Messages in this thread Patch in this message | | | Date | Fri, 24 Jun 2016 02:00:32 -0700 | From | tip-bot for Tejun Heo <> | Subject | [tip:sched/urgent] sched/core: Allow kthreads to fall back to online && !active cpus |
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Commit-ID: feb245e304f343cf5e4f9123db36354144dce8a4 Gitweb: http://git.kernel.org/tip/feb245e304f343cf5e4f9123db36354144dce8a4 Author: Tejun Heo <htejun@gmail.com> AuthorDate: Thu, 16 Jun 2016 15:35:04 -0400 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Fri, 24 Jun 2016 08:26:53 +0200
sched/core: Allow kthreads to fall back to online && !active cpus
During CPU hotplug, CPU_ONLINE callbacks are run while the CPU is online but not active. A CPU_ONLINE callback may create or bind a kthread so that its cpus_allowed mask only allows the CPU which is being brought online. The kthread may start executing before the CPU is made active and can end up in select_fallback_rq().
In such cases, the expected behavior is selecting the CPU which is coming online; however, because select_fallback_rq() only chooses from active CPUs, it determines that the task doesn't have any viable CPU in its allowed mask and ends up overriding it to cpu_possible_mask.
CPU_ONLINE callbacks should be able to put kthreads on the CPU which is coming online. Update select_fallback_rq() so that it follows cpu_online() rather than cpu_active() for kthreads.
Reported-by: Gautham R Shenoy <ego@linux.vnet.ibm.com> Tested-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Abdul Haleem <abdhalee@linux.vnet.ibm.com> Cc: Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@fb.com Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/r/20160616193504.GB3262@mtj.duckdns.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/sched/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4135ac8..51d7105 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1536,7 +1536,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p) for (;;) { /* Any allowed, online CPU? */ for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) { - if (!cpu_active(dest_cpu)) + if (!(p->flags & PF_KTHREAD) && !cpu_active(dest_cpu)) + continue; + if (!cpu_online(dest_cpu)) continue; goto out; }
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