cpu: Defer smpboot kthread unparking until CPU known to scheduler
Currently, smpboot_unpark_threads() is invoked before the incoming CPU
has been added to the scheduler's runqueue structures. This might
potentially cause the unparked kthread to run on the wrong CPU, since the
correct CPU isn't fully set up yet.
That causes a sporadic, hard to debug boot crash triggering on some
systems, reported by Borislav Petkov, and bisected down to:
2a442c9c6453 ("x86: Use common outgoing-CPU-notification code")
This patch places smpboot_unpark_threads() in a CPU hotplug
notifier with priority set so that these kthreads are unparked just after
the CPU has been added to the runqueues.
Reported-and-tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index d028721..091badf 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -73,6 +73,7 @@
/* migration should happen before other stuff but after perf */
CPU_PRI_PERF = 20,
CPU_PRI_MIGRATION = 10,
+ CPU_PRI_SMPBOOT = 9,
/* bring up workqueues before normal notifiers and down after */
CPU_PRI_WORKQUEUE_UP = 5,
CPU_PRI_WORKQUEUE_DOWN = -5,
@@ -165,6 +166,7 @@
}
#endif
+void smpboot_thread_init(void);
int cpu_up(unsigned int cpu);
void notify_cpu_starting(unsigned int cpu);
extern void cpu_maps_update_begin(void);