From:   "Uladzislau Rezki (Sony)" <urezki@gmail.com>
To:     Theodore Ts'o <tytso@mit.edu>,
        Joel Fernandes <joel@joelfernandes.org>
Cc:     RCU <rcu@vger.kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Uladzislau Rezki <urezki@gmail.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        linux-ext4@vger.kernel.org, Lukas Czerner <lczerner@redhat.com>,
        Andreas Dilger <adilger.kernel@dilger.ca>
Subject: [PATCH 1/1] ext4: Replace ext4_kvfree_array_rcu() by kvfree_rcu_mightsleep()
Date:   Fri, 17 Mar 2023 08:15:58 +0100
Message-Id: <20230317071558.335645-1-urezki@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The ext4_kvfree_array_rcu() function was introduced in order to
release some memory after a grace period during resizing of a
partition. An object that is freed does not contain any rcu_head
filed.

To do so, it requires to allocate some extra memory for a special
structure that has an rcu_head filed and pointer one where a freed
memory is attached. Finally call_rcu() API is invoked.

Since we have a single argument of kvfree_rcu() API, we can easily
replace all that tricky code by one single call that does the same
but in more efficient way.

Cc: linux-ext4@vger.kernel.org
Cc: Lukas Czerner <lczerner@redhat.com>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 fs/ext4/ext4.h    |  1 -
 fs/ext4/mballoc.c |  2 +-
 fs/ext4/resize.c  | 31 ++-----------------------------
 fs/ext4/super.c   |  2 +-
 4 files changed, 4 insertions(+), 32 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 140e1eb300d1..e43d1a2d175e 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3057,7 +3057,6 @@ extern int ext4_generic_delete_entry(struct inode *dir,
 extern bool ext4_empty_dir(struct inode *inode);
 
 /* resize.c */
-extern void ext4_kvfree_array_rcu(void *to_free);
 extern int ext4_group_add(struct super_block *sb,
 				struct ext4_new_group_data *input);
 extern int ext4_group_extend(struct super_block *sb,
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5b2ae37a8b80..96b4e3317640 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3055,7 +3055,7 @@ int ext4_mb_alloc_groupinfo(struct super_block *sb, ext4_group_t ngroups)
 	rcu_assign_pointer(sbi->s_group_info, new_groupinfo);
 	sbi->s_group_info_size = size / sizeof(*sbi->s_group_info);
 	if (old_groupinfo)
-		ext4_kvfree_array_rcu(old_groupinfo);
+		kvfree_rcu_mightsleep(old_groupinfo);
 	ext4_debug("allocated s_groupinfo array for %d meta_bg's\n",
 		   sbi->s_group_info_size);
 	return 0;
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 6b91443d6bf3..330b81f36e10 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -18,33 +18,6 @@
 
 #include "ext4_jbd2.h"
 
-struct ext4_rcu_ptr {
-	struct rcu_head rcu;
-	void *ptr;
-};
-
-static void ext4_rcu_ptr_callback(struct rcu_head *head)
-{
-	struct ext4_rcu_ptr *ptr;
-
-	ptr = container_of(head, struct ext4_rcu_ptr, rcu);
-	kvfree(ptr->ptr);
-	kfree(ptr);
-}
-
-void ext4_kvfree_array_rcu(void *to_free)
-{
-	struct ext4_rcu_ptr *ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
-
-	if (ptr) {
-		ptr->ptr = to_free;
-		call_rcu(&ptr->rcu, ext4_rcu_ptr_callback);
-		return;
-	}
-	synchronize_rcu();
-	kvfree(to_free);
-}
-
 int ext4_resize_begin(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -931,7 +904,7 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
 	n_group_desc[gdb_num] = gdb_bh;
 	rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
 	EXT4_SB(sb)->s_gdb_count++;
-	ext4_kvfree_array_rcu(o_group_desc);
+	kvfree_rcu_mightsleep(o_group_desc);
 
 	lock_buffer(EXT4_SB(sb)->s_sbh);
 	le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
@@ -994,7 +967,7 @@ static int add_new_gdb_meta_bg(struct super_block *sb,
 
 	rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
 	EXT4_SB(sb)->s_gdb_count++;
-	ext4_kvfree_array_rcu(o_group_desc);
+	kvfree_rcu_mightsleep(o_group_desc);
 	return err;
 }
 
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 87aa23d047c9..34d802848d6d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3108,7 +3108,7 @@ int ext4_alloc_flex_bg_array(struct super_block *sb, ext4_group_t ngroup)
 	rcu_assign_pointer(sbi->s_flex_groups, new_groups);
 	sbi->s_flex_groups_allocated = size;
 	if (old_groups)
-		ext4_kvfree_array_rcu(old_groups);
+		kvfree_rcu_mightsleep(old_groups);
 	return 0;
 }
 
-- 
2.30.2