[PATCH] fs: fix ups and tidy ups to /proc/filesystems caching

[Mateusz Guzik]

- add missing unlocks in some corner cases
- whitespace touch ups
- s/smp_store_release/rcu_assign_pointer/ [nop, the macro expands to the same thing]
- mark file_systems_string as __read_mostly

Signed-off-by: Mateusz Guzik <mjguzik@xxxxxxxxx>
---

Preferably this will get folded into the patch which introduces caching
to begin with, I'm posting a "full patch" just in case a separate entry
is preferred.

 fs/filesystems.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index 771fc31a69b8..673a03b5f32b 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -54,7 +54,7 @@ struct file_systems_string {
 };
 
 static unsigned long file_systems_gen;
-static struct file_systems_string __rcu *file_systems_string;
+static struct file_systems_string __read_mostly __rcu *file_systems_string;
 
 static void invalidate_filesystems_string(void);
 #else
@@ -269,7 +269,7 @@ static __cold noinline int regen_filesystems_string(void)
 	hlist_for_each_entry_rcu(p, &file_systems, list) {
 		if (!(p->fs_flags & FS_REQUIRES_DEV))
 			newlen += strlen("nodev");
-		newlen += strlen("\t") + strlen(p->name) +  strlen("\n");
+		newlen += strlen("\t") + strlen(p->name) + strlen("\n");
 	}
 	spin_unlock(&file_systems_lock);
 
@@ -289,6 +289,7 @@ static __cold noinline int regen_filesystems_string(void)
 	 * Did someone beat us to it?
 	 */
 	if (old && old->gen == file_systems_gen) {
+		spin_unlock(&file_systems_lock);
 		kfree(new);
 		return 0;
 	}
@@ -297,6 +298,7 @@ static __cold noinline int regen_filesystems_string(void)
 	 * Did the list change in the meantime?
 	 */
 	if (gen != file_systems_gen) {
+		spin_unlock(&file_systems_lock);
 		kfree(new);
 		goto retry;
 	}
@@ -321,15 +323,11 @@ static __cold noinline int regen_filesystems_string(void)
 		 * generation above and messes it up.
 		 */
 		spin_unlock(&file_systems_lock);
-		if (old)
-			kfree_rcu(old, rcu);
+		kfree(new);
 		return -EINVAL;
 	}
 
-	/*
-	 * Paired with consume fence in READ_ONCE() in filesystems_proc_show()
-	 */
-	smp_store_release(&file_systems_string, new);
+	rcu_assign_pointer(file_systems_string, new);
 	spin_unlock(&file_systems_lock);
 	if (old)
 		kfree_rcu(old, rcu);
-- 
2.48.1