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

[Khalid Aziz <khalid.aziz@oracle.com>]

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@oracle.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