Replace BKL with superblock lock in fat/msdos/vfat

This replaces the use of the BKL in the FAT family of filesystems with the
existing superblock lock instead.

The code already appears to do mostly proper locking with its own private
spinlocks (and mutexes), but while the BKL could possibly have been
dropped entirely, converting it to use the superblock lock (which is just
a regular mutex) is the conservative thing to do.

As a per-filesystem mutex, it not only won't have any of the possible
latency issues related to the BKL, but the lock is obviously private to
the particular filesystem instance and will thus not cause problems for
entirely unrelated users like the BKL can.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 19 insertions, 16 deletions

diff --git a/fs/vfat/namei.c b/fs/vfat/namei.c
index a3522727ea5..b546ba69be8 100644
--- a/fs/vfat/namei.c
+++ b/fs/vfat/namei.c
@@ -645,7 +645,7 @@ static int vfat_add_entry(struct inode *dir, struct qstr *qname, int is_dir,
 	if (len == 0)
 		return -ENOENT;
 
-	slots = kmalloc(sizeof(*slots) * MSDOS_SLOTS, GFP_KERNEL);
+	slots = kmalloc(sizeof(*slots) * MSDOS_SLOTS, GFP_NOFS);
 	if (slots == NULL)
 		return -ENOMEM;
 
@@ -687,7 +687,7 @@ static struct dentry *vfat_lookup(struct inode *dir, struct dentry *dentry,
 	struct dentry *alias;
 	int err, table;
 
-	lock_kernel();
+	lock_super(sb);
 	table = (MSDOS_SB(sb)->options.name_check == 's') ? 2 : 0;
 	dentry->d_op = &vfat_dentry_ops[table];
 
@@ -699,7 +699,7 @@ static struct dentry *vfat_lookup(struct inode *dir, struct dentry *dentry,
 	inode = fat_build_inode(sb, sinfo.de, sinfo.i_pos);
 	brelse(sinfo.bh);
 	if (IS_ERR(inode)) {
-		unlock_kernel();
+		unlock_super(sb);
 		return ERR_CAST(inode);
 	}
 	alias = d_find_alias(inode);
@@ -708,13 +708,13 @@ static struct dentry *vfat_lookup(struct inode *dir, struct dentry *dentry,
 			dput(alias);
 		else {
 			iput(inode);
-			unlock_kernel();
+			unlock_super(sb);
 			return alias;
 		}
 
 	}
 error:
-	unlock_kernel();
+	unlock_super(sb);
 	dentry->d_op = &vfat_dentry_ops[table];
 	dentry->d_time = dentry->d_parent->d_inode->i_version;
 	dentry = d_splice_alias(inode, dentry);
@@ -734,7 +734,7 @@ static int vfat_create(struct inode *dir, struct dentry *dentry, int mode,
 	struct timespec ts;
 	int err;
 
-	lock_kernel();
+	lock_super(sb);
 
 	ts = CURRENT_TIME_SEC;
 	err = vfat_add_entry(dir, &dentry->d_name, 0, 0, &ts, &sinfo);
@@ -755,17 +755,18 @@ static int vfat_create(struct inode *dir, struct dentry *dentry, int mode,
 	dentry->d_time = dentry->d_parent->d_inode->i_version;
 	d_instantiate(dentry, inode);
 out:
-	unlock_kernel();
+	unlock_super(sb);
 	return err;
 }
 
 static int vfat_rmdir(struct inode *dir, struct dentry *dentry)
 {
 	struct inode *inode = dentry->d_inode;
+	struct super_block *sb = dir->i_sb;
 	struct fat_slot_info sinfo;
 	int err;
 
-	lock_kernel();
+	lock_super(sb);
 
 	err = fat_dir_empty(inode);
 	if (err)
@@ -783,7 +784,7 @@ static int vfat_rmdir(struct inode *dir, struct dentry *dentry)
 	inode->i_mtime = inode->i_atime = CURRENT_TIME_SEC;
 	fat_detach(inode);
 out:
-	unlock_kernel();
+	unlock_super(sb);
 
 	return err;
 }
@@ -791,10 +792,11 @@ out:
 static int vfat_unlink(struct inode *dir, struct dentry *dentry)
 {
 	struct inode *inode = dentry->d_inode;
+	struct super_block *sb = dir->i_sb;
 	struct fat_slot_info sinfo;
 	int err;
 
-	lock_kernel();
+	lock_super(sb);
 
 	err = vfat_find(dir, &dentry->d_name, &sinfo);
 	if (err)
@@ -807,7 +809,7 @@ static int vfat_unlink(struct inode *dir, struct dentry *dentry)
 	inode->i_mtime = inode->i_atime = CURRENT_TIME_SEC;
 	fat_detach(inode);
 out:
-	unlock_kernel();
+	unlock_super(sb);
 
 	return err;
 }
@@ -820,7 +822,7 @@ static int vfat_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	struct timespec ts;
 	int err, cluster;
 
-	lock_kernel();
+	lock_super(sb);
 
 	ts = CURRENT_TIME_SEC;
 	cluster = fat_alloc_new_dir(dir, &ts);
@@ -849,13 +851,13 @@ static int vfat_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	dentry->d_time = dentry->d_parent->d_inode->i_version;
 	d_instantiate(dentry, inode);
 
-	unlock_kernel();
+	unlock_super(sb);
 	return 0;
 
 out_free:
 	fat_free_clusters(dir, cluster);
 out:
-	unlock_kernel();
+	unlock_super(sb);
 	return err;
 }
 
@@ -869,11 +871,12 @@ static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
 	struct timespec ts;
 	loff_t dotdot_i_pos, new_i_pos;
 	int err, is_dir, update_dotdot, corrupt = 0;
+	struct super_block *sb = old_dir->i_sb;
 
 	old_sinfo.bh = sinfo.bh = dotdot_bh = NULL;
 	old_inode = old_dentry->d_inode;
 	new_inode = new_dentry->d_inode;
-	lock_kernel();
+	lock_super(sb);
 	err = vfat_find(old_dir, &old_dentry->d_name, &old_sinfo);
 	if (err)
 		goto out;
@@ -951,7 +954,7 @@ out:
 	brelse(sinfo.bh);
 	brelse(dotdot_bh);
 	brelse(old_sinfo.bh);
-	unlock_kernel();
+	unlock_super(sb);
 
 	return err;