linux-hardening - [PATCH 16/19] x86/resctrl: release rdtgroup_mutex and the CPU hotplug lock in rdt_shutdown

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Date:   Wed, 13 Sep 2023 08:10:10 -0300
From:   Christoph Hellwig <hch@....de>
To:     Christian Brauner <brauner@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Tejun Heo <tj@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Damien Le Moal <dlemoal@...nel.org>,
        Naohiro Aota <naohiro.aota@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-hardening@...r.kernel.org,
        cgroups@...r.kernel.org
Subject: [PATCH 16/19] x86/resctrl: release rdtgroup_mutex and the CPU hotplug lock in rdt_shutdown_sb

While the resctl code is a bit confusing, I can't find anything protected
by rdtgroup_mutex or the CPU hotplug lock in generic_shutdown_super or
kernfs_free_sb.  Drop the locks at the end of rdt_shutdown_sb to avoid
holding locks over method calls and VFS code which itself already has a
rather complicated locking hierarchy.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 8db767fd80df6b..e87de519493021 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2793,11 +2793,6 @@ static void rdt_shutdown_sb(struct super_block *sb)
 	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
 	static_branch_disable_cpuslocked(&rdt_enable_key);
 	kernfs_shutdown_sb(sb);
-}
-
-static void rdt_free_sb(struct super_block *sb)
-{
-	kernfs_free_sb(sb);
 	mutex_unlock(&rdtgroup_mutex);
 	cpus_read_unlock();
 }
@@ -2807,7 +2802,7 @@ static struct file_system_type rdt_fs_type = {
 	.init_fs_context	= rdt_init_fs_context,
 	.parameters		= rdt_fs_parameters,
 	.shutdown_sb		= rdt_shutdown_sb,
-	.free_sb		= rdt_free_sb,
+	.free_sb		= kernfs_free_sb,
 };
 
 static int mon_addfile(struct kernfs_node *parent_kn, const char *name,
-- 
2.39.2