Re: [PATCH 18/20] fs: remove get_super_thawed and get_super_exclusive_thawed

[Jan Kara <jack@xxxxxxx>]

On Wed 18-11-20 09:47:58, Christoph Hellwig wrote:
> Just open code the wait in the only caller of both functions.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

As far as I remember, Al (added to CC) generally objected against exporting
bits from fs/super.c (like put_super(), __get_super()) in the past. FWIW I
also find a dedicated function in fs/super.c somewhat cleaner than
opencoding in quota code but I can live with both...

                                                                Honza

> ---
>  fs/internal.h      |  2 ++
>  fs/quota/quota.c   | 31 +++++++++++++++++++++-------
>  fs/super.c         | 51 ++--------------------------------------------
>  include/linux/fs.h |  4 +---
>  4 files changed, 29 insertions(+), 59 deletions(-)
> 
> diff --git a/fs/internal.h b/fs/internal.h
> index a7cd0f64faa4ab..47be21dfeebef5 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -114,7 +114,9 @@ extern struct file *alloc_empty_file_noaccount(int, const 
> struct cred *);
>   */
>  extern int reconfigure_super(struct fs_context *);
>  extern bool trylock_super(struct super_block *sb);
> +struct super_block *__get_super(struct block_device *bdev, bool excl);
>  extern struct super_block *user_get_super(dev_t);
> +void put_super(struct super_block *sb);
>  extern bool mount_capable(struct fs_context *);
>  
>  /*
> diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> index 9af95c7a0bbe3c..f3d32b0d9008f2 100644
> --- a/fs/quota/quota.c
> +++ b/fs/quota/quota.c
> @@ -20,6 +20,7 @@
>  #include <linux/writeback.h>
>  #include <linux/nospec.h>
>  #include "compat.h"
> +#include "../internal.h"
>  
>  static int check_quotactl_permission(struct super_block *sb, int type, int 
> cmd,
>                                    qid_t id)
> @@ -868,6 +869,7 @@ static struct super_block *quotactl_block(const char 
> __user *special, int cmd)
>       struct block_device *bdev;
>       struct super_block *sb;
>       struct filename *tmp = getname(special);
> +     bool excl = false, thawed = false;
>  
>       if (IS_ERR(tmp))
>               return ERR_CAST(tmp);
> @@ -875,17 +877,32 @@ static struct super_block *quotactl_block(const char 
> __user *special, int cmd)
>       putname(tmp);
>       if (IS_ERR(bdev))
>               return ERR_CAST(bdev);
> -     if (quotactl_cmd_onoff(cmd))
> -             sb = get_super_exclusive_thawed(bdev);
> -     else if (quotactl_cmd_write(cmd))
> -             sb = get_super_thawed(bdev);
> -     else
> -             sb = get_super(bdev);
> +
> +     if (quotactl_cmd_onoff(cmd)) {
> +             excl = true;
> +             thawed = true;
> +     } else if (quotactl_cmd_write(cmd)) {
> +             thawed = true;
> +     }
> +
> +retry:
> +     sb = __get_super(bdev, excl);
> +     if (thawed && sb && sb->s_writers.frozen != SB_UNFROZEN) {
> +             if (excl)
> +                     up_write(&sb->s_umount);
> +             else
> +                     up_read(&sb->s_umount);
> +             wait_event(sb->s_writers.wait_unfrozen,
> +                        sb->s_writers.frozen == SB_UNFROZEN);
> +             put_super(sb);
> +             goto retry;
> +     }
> +
>       bdput(bdev);
>       if (!sb)
>               return ERR_PTR(-ENODEV);
> -
>       return sb;
> +
>  #else
>       return ERR_PTR(-ENODEV);
>  #endif
> diff --git a/fs/super.c b/fs/super.c
> index 98bb0629ee108e..343e5c1e538d2a 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -307,7 +307,7 @@ static void __put_super(struct super_block *s)
>   *   Drops a temporary reference, frees superblock if there's no
>   *   references left.
>   */
> -static void put_super(struct super_block *sb)
> +void put_super(struct super_block *sb)
>  {
>       spin_lock(&sb_lock);
>       __put_super(sb);
> @@ -740,7 +740,7 @@ void iterate_supers_type(struct file_system_type *type,
>  
>  EXPORT_SYMBOL(iterate_supers_type);
>  
> -static struct super_block *__get_super(struct block_device *bdev, bool excl)
> +struct super_block *__get_super(struct block_device *bdev, bool excl)
>  {
>       struct super_block *sb;
>  
> @@ -789,53 +789,6 @@ struct super_block *get_super(struct block_device *bdev)
>  }
>  EXPORT_SYMBOL(get_super);
>  
> -static struct super_block *__get_super_thawed(struct block_device *bdev,
> -                                           bool excl)
> -{
> -     while (1) {
> -             struct super_block *s = __get_super(bdev, excl);
> -             if (!s || s->s_writers.frozen == SB_UNFROZEN)
> -                     return s;
> -             if (!excl)
> -                     up_read(&s->s_umount);
> -             else
> -                     up_write(&s->s_umount);
> -             wait_event(s->s_writers.wait_unfrozen,
> -                        s->s_writers.frozen == SB_UNFROZEN);
> -             put_super(s);
> -     }
> -}
> -
> -/**
> - *   get_super_thawed - get thawed superblock of a device
> - *   @bdev: device to get the superblock for
> - *
> - *   Scans the superblock list and finds the superblock of the file system
> - *   mounted on the device. The superblock is returned once it is thawed
> - *   (or immediately if it was not frozen). %NULL is returned if no match
> - *   is found.
> - */
> -struct super_block *get_super_thawed(struct block_device *bdev)
> -{
> -     return __get_super_thawed(bdev, false);
> -}
> -EXPORT_SYMBOL(get_super_thawed);
> -
> -/**
> - *   get_super_exclusive_thawed - get thawed superblock of a device
> - *   @bdev: device to get the superblock for
> - *
> - *   Scans the superblock list and finds the superblock of the file system
> - *   mounted on the device. The superblock is returned once it is thawed
> - *   (or immediately if it was not frozen) and s_umount semaphore is held
> - *   in exclusive mode. %NULL is returned if no match is found.
> - */
> -struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
> -{
> -     return __get_super_thawed(bdev, true);
> -}
> -EXPORT_SYMBOL(get_super_exclusive_thawed);
> -
>  /**
>   * get_active_super - get an active reference to the superblock of a device
>   * @bdev: device to get the superblock for
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 8667d0cdc71e76..a61df0dd4f1989 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1409,7 +1409,7 @@ enum {
>  
>  struct sb_writers {
>       int                             frozen;         /* Is sb frozen? */
> -     wait_queue_head_t               wait_unfrozen;  /* for 
> get_super_thawed() */
> +     wait_queue_head_t               wait_unfrozen;  /* wait for thaw */
>       struct percpu_rw_semaphore      rw_sem[SB_FREEZE_LEVELS];
>  };
>  
> @@ -3132,8 +3132,6 @@ extern struct file_system_type *get_filesystem(struct 
> file_system_type *fs);
>  extern void put_filesystem(struct file_system_type *fs);
>  extern struct file_system_type *get_fs_type(const char *name);
>  extern struct super_block *get_super(struct block_device *);
> -extern struct super_block *get_super_thawed(struct block_device *);
> -extern struct super_block *get_super_exclusive_thawed(struct block_device 
> *bdev);
>  extern struct super_block *get_active_super(struct block_device *bdev);
>  extern void drop_super(struct super_block *sb);
>  extern void drop_super_exclusive(struct super_block *sb);
> -- 
> 2.29.2
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR