On Fri, Mar 17, 2023 at 08:15:58AM +0100, Uladzislau Rezki (Sony) wrote:
> 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@xxxxxxxxxxxxxxx
> Cc: Lukas Czerner <lczerner@xxxxxxxxxx>
> Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
>From an RCU perspective:
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
> 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
>
