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Commit a2584e1d authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Shaohua Li <shli@fb.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
parent f57b3087

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

+3 −5
Original line number Diff line number Diff line
@@ -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);