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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 <tglx@linutronix.de>
Cc: Shaohua Li <shli@fb.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
This commit is contained in:
Thomas Gleixner 2016-11-15 15:12:13 +01:00
parent f57b308728
commit a2584e1d5a
1 changed files with 3 additions and 5 deletions
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8
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
View File

@ -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);