From dfd718a2ed1f678e66749ffe41bdeafedf3f4314 Mon Sep 17 00:00:00 2001 From: "Gautham R. Shenoy" Date: Mon, 1 Oct 2018 16:10:39 +0530 Subject: [PATCH] powerpc/rtas: Fix a potential race between CPU-Offline & Migration Live Partition Migrations require all the present CPUs to execute the H_JOIN call, and hence rtas_ibm_suspend_me() onlines any offline CPUs before initiating the migration for this purpose. The commit 85a88cabad57 ("powerpc/pseries: Disable CPU hotplug across migrations") disables any CPU-hotplug operations once all the offline CPUs are brought online to prevent any further state change. Once the CPU-Hotplug operation is disabled, the code assumes that all the CPUs are online. However, there is a minor window in rtas_ibm_suspend_me() between onlining the offline CPUs and disabling CPU-Hotplug when a concurrent CPU-offline operations initiated by the userspace can succeed thereby nullifying the the aformentioned assumption. In this unlikely case these offlined CPUs will not call H_JOIN, resulting in a system hang. Fix this by verifying that all the present CPUs are actually online after CPU-Hotplug has been disabled, failing which we restore the state of the offline CPUs in rtas_ibm_suspend_me() and return an -EBUSY. Cc: Nathan Fontenot Cc: Tyrel Datwyler Suggested-by: Michael Ellerman Signed-off-by: Gautham R. Shenoy Reviewed-by: Nathan Fontenot Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/rtas.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c index e02ac377ed64..de35bd8f047f 100644 --- a/arch/powerpc/kernel/rtas.c +++ b/arch/powerpc/kernel/rtas.c @@ -983,6 +983,14 @@ int rtas_ibm_suspend_me(u64 handle) cpu_hotplug_disable(); + /* Check if we raced with a CPU-Offline Operation */ + if (unlikely(!cpumask_equal(cpu_present_mask, cpu_online_mask))) { + pr_err("%s: Raced against a concurrent CPU-Offline\n", + __func__); + atomic_set(&data.error, -EBUSY); + goto out_hotplug_enable; + } + /* Call function on all CPUs. One of us will make the * rtas call */ @@ -994,6 +1002,7 @@ int rtas_ibm_suspend_me(u64 handle) if (atomic_read(&data.error) != 0) printk(KERN_ERR "Error doing global join\n"); +out_hotplug_enable: cpu_hotplug_enable(); /* Take down CPUs not online prior to suspend */ -- 2.20.1