From a2584e1d5a74e8f5387d6484ad4c73ded36aa2ae Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 15 Nov 2016 15:12:13 +0100 Subject: [PATCH] x86/intel_rdt: Prevent deadlock against hotplug lock The cpu online/offline callbacks of intel_rdt lock rdtgroup_mutex nested inside of cpu hotplug lock. rdtgroup_cpus_write() does it in reverse order. Remove the get/put_online_cpus() calls from rdtgroup_cpus_write(). This is safe against cpu hotplug as the resource group cpumasks are protected by rdtgroup_mutex. Found by review, but should have been found if authors would have bothered to test cpu hotplug with lockdep enabled. Signed-off-by: Thomas Gleixner Cc: Shaohua Li Cc: Fenghua Yu Cc: Tony Luck --- arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c index cff286e6d69f..2f54931e0fa9 100644 --- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c +++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c @@ -207,6 +207,7 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of, free_cpumask_var(tmpmask); return -ENOMEM; } + rdtgrp = rdtgroup_kn_lock_live(of->kn); if (!rdtgrp) { ret = -ENOENT; @@ -217,12 +218,11 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of, if (ret) goto unlock; - get_online_cpus(); /* check that user didn't specify any offline cpus */ cpumask_andnot(tmpmask, newmask, cpu_online_mask); if (cpumask_weight(tmpmask)) { ret = -EINVAL; - goto end; + goto unlock; } /* Check whether cpus are dropped from this group */ @@ -231,7 +231,7 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of, /* Can't drop from default group */ if (rdtgrp == &rdtgroup_default) { ret = -EINVAL; - goto end; + goto unlock; } /* Give any dropped cpus to rdtgroup_default */ cpumask_or(&rdtgroup_default.cpu_mask, @@ -258,8 +258,6 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of, /* Done pushing/pulling - update this group with new mask */ cpumask_copy(&rdtgrp->cpu_mask, newmask); -end: - put_online_cpus(); unlock: rdtgroup_kn_unlock(of->kn); free_cpumask_var(tmpmask); -- 2.25.1