Multiple people have balked at the the fact that
super_lock{_shared,_excluse}() return booleans and even if they return
false hold s_umount. So let's change them to only hold s_umount when
true is returned and change the code accordingly.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
fs/super.c | 105 +++++++++++++++++++++++++++++++++++--------------------------
1 file changed, 61 insertions(+), 44 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index c7b452e12e4c..9cf3ee50cecd 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -105,8 +105,9 @@ static inline bool wait_born(struct super_block *sb)
*
* The caller must have acquired a temporary reference on @sb->s_count.
*
- * Return: This returns true if SB_BORN was set, false if SB_DYING was
- * set. The function acquires s_umount and returns with it held.
+ * Return: The function returns true if SB_BORN was set and with
+ * s_umount held. The function returns false if SB_DYING was
+ * set and without s_umount held.
*/
static __must_check bool super_lock(struct super_block *sb, bool excl)
{
@@ -121,8 +122,10 @@ static __must_check bool super_lock(struct super_block *sb, bool excl)
* @sb->s_root is NULL and @sb->s_active is 0. No one needs to
* grab a reference to this. Tell them so.
*/
- if (sb->s_flags & SB_DYING)
+ if (sb->s_flags & SB_DYING) {
+ super_unlock(sb, excl);
return false;
+ }
/* Has called ->get_tree() successfully. */
if (sb->s_flags & SB_BORN)
@@ -140,13 +143,13 @@ static __must_check bool super_lock(struct super_block *sb, bool excl)
goto relock;
}
-/* wait and acquire read-side of @sb->s_umount */
+/* wait and try to acquire read-side of @sb->s_umount */
static inline bool super_lock_shared(struct super_block *sb)
{
return super_lock(sb, false);
}
-/* wait and acquire write-side of @sb->s_umount */
+/* wait and try to acquire write-side of @sb->s_umount */
static inline bool super_lock_excl(struct super_block *sb)
{
return super_lock(sb, true);
@@ -532,16 +535,18 @@ EXPORT_SYMBOL(deactivate_super);
*/
static int grab_super(struct super_block *s) __releases(sb_lock)
{
- bool born;
+ bool locked;
s->s_count++;
spin_unlock(&sb_lock);
- born = super_lock_excl(s);
- if (born && atomic_inc_not_zero(&s->s_active)) {
- put_super(s);
- return 1;
+ locked = super_lock_excl(s);
+ if (locked) {
+ if (atomic_inc_not_zero(&s->s_active)) {
+ put_super(s);
+ return 1;
+ }
+ super_unlock_excl(s);
}
- super_unlock_excl(s);
put_super(s);
return 0;
}
@@ -572,7 +577,6 @@ static inline bool wait_dead(struct super_block *sb)
*/
static bool grab_super_dead(struct super_block *sb)
{
-
sb->s_count++;
if (grab_super(sb)) {
put_super(sb);
@@ -958,15 +962,17 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
spin_lock(&sb_lock);
list_for_each_entry(sb, &super_blocks, s_list) {
- bool born;
+ bool locked;
sb->s_count++;
spin_unlock(&sb_lock);
- born = super_lock_shared(sb);
- if (born && sb->s_root)
- f(sb, arg);
- super_unlock_shared(sb);
+ locked = super_lock_shared(sb);
+ if (locked) {
+ if (sb->s_root)
+ f(sb, arg);
+ super_unlock_shared(sb);
+ }
spin_lock(&sb_lock);
if (p)
@@ -994,15 +1000,17 @@ void iterate_supers_type(struct file_system_type *type,
spin_lock(&sb_lock);
hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
- bool born;
+ bool locked;
sb->s_count++;
spin_unlock(&sb_lock);
- born = super_lock_shared(sb);
- if (born && sb->s_root)
- f(sb, arg);
- super_unlock_shared(sb);
+ locked = super_lock_shared(sb);
+ if (locked) {
+ if (sb->s_root)
+ f(sb, arg);
+ super_unlock_shared(sb);
+ }
spin_lock(&sb_lock);
if (p)
@@ -1051,15 +1059,17 @@ struct super_block *user_get_super(dev_t dev, bool excl)
spin_lock(&sb_lock);
list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_dev == dev) {
- bool born;
+ bool locked;
sb->s_count++;
spin_unlock(&sb_lock);
/* still alive? */
- born = super_lock(sb, excl);
- if (born && sb->s_root)
- return sb;
- super_unlock(sb, excl);
+ locked = super_lock(sb, excl);
+ if (locked) {
+ if (sb->s_root)
+ return sb;
+ super_unlock(sb, excl);
+ }
/* nope, got unmounted */
spin_lock(&sb_lock);
__put_super(sb);
@@ -1170,9 +1180,9 @@ int reconfigure_super(struct fs_context *fc)
static void do_emergency_remount_callback(struct super_block *sb)
{
- bool born = super_lock_excl(sb);
+ bool locked = super_lock_excl(sb);
- if (born && sb->s_root && sb->s_bdev && !sb_rdonly(sb)) {
+ if (locked && sb->s_root && sb->s_bdev && !sb_rdonly(sb)) {
struct fs_context *fc;
fc = fs_context_for_reconfigure(sb->s_root,
@@ -1183,7 +1193,8 @@ static void do_emergency_remount_callback(struct super_block *sb)
put_fs_context(fc);
}
}
- super_unlock_excl(sb);
+ if (locked)
+ super_unlock_excl(sb);
}
static void do_emergency_remount(struct work_struct *work)
@@ -1206,16 +1217,17 @@ void emergency_remount(void)
static void do_thaw_all_callback(struct super_block *sb)
{
- bool born = super_lock_excl(sb);
+ bool locked = super_lock_excl(sb);
- if (born && sb->s_root) {
+ if (locked && sb->s_root) {
if (IS_ENABLED(CONFIG_BLOCK))
while (sb->s_bdev && !thaw_bdev(sb->s_bdev))
pr_warn("Emergency Thaw on %pg\n", sb->s_bdev);
thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE);
- } else {
- super_unlock_excl(sb);
+ return;
}
+ if (locked)
+ super_unlock_excl(sb);
}
static void do_thaw_all(struct work_struct *work)
@@ -1429,7 +1441,7 @@ static struct super_block *bdev_super_lock_shared(struct block_device *bdev)
__releases(&bdev->bd_holder_lock)
{
struct super_block *sb = bdev->bd_holder;
- bool born;
+ bool locked;
lockdep_assert_held(&bdev->bd_holder_lock);
lockdep_assert_not_held(&sb->s_umount);
@@ -1441,9 +1453,8 @@ static struct super_block *bdev_super_lock_shared(struct block_device *bdev)
spin_unlock(&sb_lock);
mutex_unlock(&bdev->bd_holder_lock);
- born = super_lock_shared(sb);
- if (!born || !sb->s_root || !(sb->s_flags & SB_ACTIVE)) {
- super_unlock_shared(sb);
+ locked = super_lock_shared(sb);
+ if (!locked || !sb->s_root || !(sb->s_flags & SB_ACTIVE)) {
put_super(sb);
return NULL;
}
@@ -1959,9 +1970,11 @@ int freeze_super(struct super_block *sb, enum freeze_holder who)
{
int ret;
+ if (!super_lock_excl(sb)) {
+ WARN_ON_ONCE("Dying superblock while freezing!");
+ return -EINVAL;
+ }
atomic_inc(&sb->s_active);
- if (!super_lock_excl(sb))
- WARN(1, "Dying superblock while freezing!");
retry:
if (sb->s_writers.frozen == SB_FREEZE_COMPLETE) {
@@ -2009,8 +2022,10 @@ int freeze_super(struct super_block *sb, enum freeze_holder who)
/* Release s_umount to preserve sb_start_write -> s_umount ordering */
super_unlock_excl(sb);
sb_wait_write(sb, SB_FREEZE_WRITE);
- if (!super_lock_excl(sb))
- WARN(1, "Dying superblock while freezing!");
+ if (!super_lock_excl(sb)) {
+ WARN_ON_ONCE("Dying superblock while freezing!");
+ return -EINVAL;
+ }
/* Now we go and block page faults... */
sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
@@ -2128,8 +2143,10 @@ static int thaw_super_locked(struct super_block *sb, enum freeze_holder who)
*/
int thaw_super(struct super_block *sb, enum freeze_holder who)
{
- if (!super_lock_excl(sb))
- WARN(1, "Dying superblock while thawing!");
+ if (!super_lock_excl(sb)) {
+ WARN_ON_ONCE("Dying superblock while thawing!");
+ return -EINVAL;
+ }
return thaw_super_locked(sb, who);
}
EXPORT_SYMBOL(thaw_super);
--
2.34.1
