linux-kernel - [PATCH v1 05/14] mm/mshare: Add locking to msharefs syscalls

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Date:   Mon, 11 Apr 2022 10:05:49 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     akpm@...ux-foundation.org, willy@...radead.org
Cc:     Khalid Aziz <khalid.aziz@...cle.com>, aneesh.kumar@...ux.ibm.com,
        arnd@...db.de, 21cnbao@...il.com, corbet@....net,
        dave.hansen@...ux.intel.com, david@...hat.com,
        ebiederm@...ssion.com, hagen@...u.net, jack@...e.cz,
        keescook@...omium.org, kirill@...temov.name, kucharsk@...il.com,
        linkinjeon@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        longpeng2@...wei.com, luto@...nel.org, markhemm@...glemail.com,
        pcc@...gle.com, rppt@...nel.org, sieberf@...zon.com,
        sjpark@...zon.de, surenb@...gle.com, tst@...oebel-theuer.de,
        yzaikin@...gle.com
Subject: [PATCH v1 05/14] mm/mshare: Add locking to msharefs syscalls

Lock the root inode for msharefs when creating a new file or
deleting an existing one to avoid races. mshare syscalls are low
frequency operations, so locking the root inode is reasonable.

Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
---
 mm/mshare.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index b9d7836f9bd1..85ccb7f02f33 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -195,11 +195,12 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
 	err = msharefs_d_hash(msharefs_sb->s_root, &namestr);
 	if (err)
 		goto err_out;
+	inode_lock(d_inode(msharefs_sb->s_root));
 	dentry = d_lookup(msharefs_sb->s_root, &namestr);
 	if (dentry && (oflag & (O_EXCL|O_CREAT))) {
 		err = -EEXIST;
 		dput(dentry);
-		goto err_out;
+		goto err_unlock_inode;
 	}
 
 	if (dentry) {
@@ -232,6 +233,7 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
 			goto err_relinfo;
 	}
 
+	inode_unlock(d_inode(msharefs_sb->s_root));
 	putname(fname);
 	return 0;
 
@@ -239,6 +241,8 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
 	kfree(info);
 err_relmm:
 	mmput(mm);
+err_unlock_inode:
+	inode_unlock(d_inode(msharefs_sb->s_root));
 err_out:
 	putname(fname);
 	return err;
@@ -264,10 +268,11 @@ SYSCALL_DEFINE1(mshare_unlink, const char *, name)
 	err = msharefs_d_hash(msharefs_sb->s_root, &namestr);
 	if (err)
 		goto err_out;
+	inode_lock(d_inode(msharefs_sb->s_root));
 	dentry = d_lookup(msharefs_sb->s_root, &namestr);
 	if (dentry == NULL) {
 		err = -EINVAL;
-		goto err_out;
+		goto err_unlock_inode;
 	}
 
 	inode = d_inode(dentry);
@@ -290,11 +295,14 @@ SYSCALL_DEFINE1(mshare_unlink, const char *, name)
 		dput(dentry);
 	}
 
+	inode_unlock(d_inode(msharefs_sb->s_root));
 	putname(fname);
 	return 0;
 
 err_dput:
 	dput(dentry);
+err_unlock_inode:
+	inode_unlock(d_inode(msharefs_sb->s_root));
 err_out:
 	putname(fname);
 	return err;
-- 
2.32.0