Commit-ID: a2584e1d5a74e8f5387d6484ad4c73ded36aa2ae
Gitweb: http://git.kernel.org/tip/a2584e1d5a74e8f5387d6484ad4c73ded36aa2ae
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Tue, 15 Nov 2016 15:12:13 +0100
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 15 Nov 2016 18:35:49 +0100
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@xxxxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
---
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 cff286e..2f54931 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);
--
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