linux-kernel - [tip:x86/urgent] x86/intel_rdt: Put group node in rdtgroup_kn

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Message-ID: <tip-49ec8f5b6ae3ab60385492cad900ffc8a523c895@git.kernel.org>
Date:   Tue, 14 Mar 2017 13:55:16 -0700
From:   tip-bot for Jiri Olsa <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, tglx@...utronix.de, peterz@...radead.org,
        fenghua.yu@...el.com, shli@...com, a.p.zijlstra@...llo.nl,
        linux-kernel@...r.kernel.org, mingo@...nel.org, efault@....de,
        jolsa@...nel.org
Subject: [tip:x86/urgent] x86/intel_rdt: Put group node in
 rdtgroup_kn_unlock

Commit-ID:  49ec8f5b6ae3ab60385492cad900ffc8a523c895
Gitweb:     http://git.kernel.org/tip/49ec8f5b6ae3ab60385492cad900ffc8a523c895
Author:     Jiri Olsa <jolsa@...nel.org>
AuthorDate: Tue, 14 Mar 2017 15:20:53 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 14 Mar 2017 21:51:58 +0100

x86/intel_rdt: Put group node in rdtgroup_kn_unlock

The rdtgroup_kn_unlock waits for the last user to release and put its
node. But it's calling kernfs_put on the node which calls the
rdtgroup_kn_unlock, which might not be the group's directory node, but
another group's file node.

This race could be easily reproduced by running 2 instances
of following script:

  mount -t resctrl resctrl /sys/fs/resctrl/
  pushd /sys/fs/resctrl/
  mkdir krava
  echo "krava" > krava/schemata
  rmdir krava
  popd
  umount  /sys/fs/resctrl

It triggers the slub debug error message with following command
line config: slub_debug=,kernfs_node_cache.

Call kernfs_put on the group's node to fix it.

Fixes: 60cf5e101fd4 ("x86/intel_rdt: Add mkdir to resctrl file system")
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mike Galbraith <efault@....de>
Cc: Shaohua Li <shli@...com>
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/1489501253-20248-1-git-send-email-jolsa@kernel.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index c05509d..9ac2a5c 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -727,7 +727,7 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
 	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
 	    (rdtgrp->flags & RDT_DELETED)) {
 		kernfs_unbreak_active_protection(kn);
-		kernfs_put(kn);
+		kernfs_put(rdtgrp->kn);
 		kfree(rdtgrp);
 	} else {
 		kernfs_unbreak_active_protection(kn);