linux-hardening - [PATCH 08/19] pstore: shrink the pstore_sb_lock critical section in pstore_kill

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Date:   Wed, 13 Sep 2023 08:10:02 -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 08/19] pstore: shrink the pstore_sb_lock critical section in pstore_kill_sb

->kill_sb can't race with creating ->fill_super because pstore is a
_single file system that only ever has a single sb instance, and we wait
for the previous one to go away before creating a new one.  Reduce
the critical section so that is is not held over generic_shutdown_super.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 fs/pstore/inode.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index 585360706b335f..fd1d24b47160d0 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -467,10 +467,9 @@ static struct dentry *pstore_mount(struct file_system_type *fs_type,
 
 static void pstore_kill_sb(struct super_block *sb)
 {
-	mutex_lock(&pstore_sb_lock);
-	WARN_ON(pstore_sb && pstore_sb != sb);
-
 	kill_litter_super(sb);
+
+	mutex_lock(&pstore_sb_lock);
 	pstore_sb = NULL;
 
 	mutex_lock(&records_list_lock);
-- 
2.39.2