super: use common iterator (Part 2)

Use a common iterator for all callbacks. We could go for something even
more elaborate (advance step-by-step similar to iov_iter) but I really
don't think this is warranted.

Link: https://lore.kernel.org/r/20250329-work-freeze-v2-5-a47af37ecc3d@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/super.c b/fs/super.c
index 0dd208804a74d9794cce927ece51b56a4653b71c..796e7f402a413b72b5bcc8088ef7ff6ce0677ec2 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -887,21 +887,46 @@ void drop_super_exclusive(struct super_block *sb)
 }
 EXPORT_SYMBOL(drop_super_exclusive);
 
-void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl)
+enum super_iter_flags_t {
+       SUPER_ITER_EXCL         = (1U << 0),
+       SUPER_ITER_UNLOCKED     = (1U << 1),
+       SUPER_ITER_REVERSE      = (1U << 2),
+};
+
+static inline struct super_block *first_super(enum super_iter_flags_t flags)
+{
+       if (flags & SUPER_ITER_REVERSE)
+               return list_last_entry(&super_blocks, struct super_block, s_list);
+       return list_first_entry(&super_blocks, struct super_block, s_list);
+}
+
+static inline struct super_block *next_super(struct super_block *sb,
+                                            enum super_iter_flags_t flags)
+{
+       if (flags & SUPER_ITER_REVERSE)
+               return list_prev_entry(sb, s_list);
+       return list_next_entry(sb, s_list);
+}
+
+static void __iterate_supers(void (*f)(struct super_block *, void *), void *arg,
+                            enum super_iter_flags_t flags)
 {
        struct super_block *sb, *p = NULL;
+       bool excl = flags & SUPER_ITER_EXCL;
 
-       spin_lock(&sb_lock);
-       list_for_each_entry(sb, &super_blocks, s_list) {
-               bool locked;
+       guard(spinlock)(&sb_lock);
 
+       for (sb = first_super(flags);
+            !list_entry_is_head(sb, &super_blocks, s_list);
+            sb = next_super(sb, flags)) {
                if (super_flags(sb, SB_DYING))
                        continue;
                sb->s_count++;
                spin_unlock(&sb_lock);
 
-               locked = super_lock(sb, excl);
-               if (locked) {
+               if (flags & SUPER_ITER_UNLOCKED) {
+                       f(sb, arg);
+               } else if (super_lock(sb, excl)) {
                        f(sb, arg);
                        super_unlock(sb, excl);
                }
@@ -913,7 +938,11 @@ void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool e
        }
        if (p)
                __put_super(p);
-       spin_unlock(&sb_lock);
+}
+
+void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+{
+       __iterate_supers(f, arg, 0);
 }
 
 /**
@@ -1097,7 +1126,8 @@ static void do_emergency_remount_callback(struct super_block *sb, void *unused)
 
 static void do_emergency_remount(struct work_struct *work)
 {
-       __iterate_supers(do_emergency_remount_callback, NULL, true);
+       __iterate_supers(do_emergency_remount_callback, NULL,
+                        SUPER_ITER_EXCL | SUPER_ITER_REVERSE);
        kfree(work);
        printk("Emergency Remount complete\n");
 }
@@ -1124,7 +1154,7 @@ static void do_thaw_all_callback(struct super_block *sb, void *unused)
 
 static void do_thaw_all(struct work_struct *work)
 {
-       __iterate_supers(do_thaw_all_callback, NULL, true);
+       __iterate_supers(do_thaw_all_callback, NULL, SUPER_ITER_EXCL);
        kfree(work);
        printk(KERN_WARNING "Emergency Thaw complete\n");
 }

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5e007bffd00e3b5e4a4f1be20ecbaa173072a5ba..96f8c8a794eabce9e5701b7c5c72a69cbb19d469 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3515,11 +3515,7 @@ extern void put_filesystem(struct file_system_type *fs);
 extern struct file_system_type *get_fs_type(const char *name);
 extern void drop_super(struct super_block *sb);
 extern void drop_super_exclusive(struct super_block *sb);
-void __iterate_supers(void (*f)(struct super_block *, void *), void *arg, bool excl);
-static inline void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
-{
-       __iterate_supers(f, arg, false);
-}
+extern void iterate_supers(void (*f)(struct super_block *, void *), void *arg);
 extern void iterate_supers_type(struct file_system_type *,
                                void (*)(struct super_block *, void *), void *);