linux-kernel - [RFC PATCH 5/6] mm: Add locking to msharefs syscalls

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Date:   Tue, 18 Jan 2022 14:19:17 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     akpm@...ux-foundation.org, willy@...radead.org,
        longpeng2@...wei.com, arnd@...db.de, dave.hansen@...ux.intel.com,
        david@...hat.com, rppt@...nel.org, surenb@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Khalid Aziz <khalid.aziz@...cle.com>
Subject: [RFC PATCH 5/6] mm: 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 8273136363cc..adfd5a280e5b 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -194,11 +194,12 @@ 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) {
@@ -231,6 +232,7 @@ 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;
 
@@ -238,6 +240,8 @@ 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;
@@ -263,10 +267,11 @@ 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);
@@ -289,11 +294,14 @@ 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