Re: [PATCH v11] ovl: Improving syncfs efficiency

[Miklos Szeredi <miklos@szeredi.hu>]

On Mon, Feb 10, 2020 at 4:10 AM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
> Current syncfs(2) syscall on overlayfs just calls sync_filesystem()
> on upper_sb to synchronize whole dirty inodes in upper filesystem
> regardless of the overlay ownership of the inode. In the use case of
> container, when multiple containers using the same underlying upper
> filesystem, it has some shortcomings as below.
>
> (1) Performance
> Synchronization is probably heavy because it actually syncs unnecessary
> inodes for target overlayfs.
>
> (2) Interference
> Unplanned synchronization will probably impact IO performance of
> unrelated container processes on the other overlayfs.
>
> This patch iterates upper inode list in overlayfs to only sync target
> dirty inodes and wait for completion. By doing this, It is able to
> reduce cost of synchronization and will not seriously impact IO performance
> of unrelated processes. In special case, when having very few dirty inodes
> and a lot of clean upper inodes in overlayfs, then iteration may waste
> time so that synchronization is slower than before, but we think the
> potential for performance improvement far surpass the potential for
> performance regression in most cases.

A possible optimization would be to only add inodes to the list that
may have been modified (e.g. opened for write, truncated, etc..).
This might not be a big win due to the fact that upper inodes are
likely those that have been recently copied up.  But as I see it, it
does not not have any drawbacks compared to adding the inode to the
list on lookup.




>
> Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
> ---
> Changes since v10:
> - Add special handling in ovl_evict_inode() for inode eviction trigered
> by kswapd memory reclamation(with PF_MEMALLOC flag).
> - Rebase on current latest overlayfs-next tree.
> - Slightly modify license information.
>
> Changes since v9:
> - Rebase on current latest overlayfs-next tree.
> - Calling clear_inode() regardless of having upper inode.
>
> Changes since v8:
> - Remove unnecessary blk_start_plug() call in ovl_sync_inodes().
>
> Changes since v7:
> - Check OVL_EVICT_PENDING flag instead of I_FREEING to recognize
> inode which is in eviction process.
> - Do not move ovl_inode back to ofs->upper_inodes when inode is in
> eviction process.
> - Delete unnecessary memory barrier in ovl_evict_inode().
>
> Changes since v6:
> - Take/release sb->s_sync_lock bofore/after sync_fs to serialize
> concurrent syncfs.
> - Change list iterating method to improve code readability.
> - Fix typo in commit log and comments.
> - Add header comment to sync.c.
>
> Changes since v5:
> - Move sync related functions to new file sync.c.
> - Introduce OVL_EVICT_PENDING flag to avoid race conditions.
> - If ovl inode flag is I_WILL_FREE or I_FREEING then syncfs
> will wait until OVL_EVICT_PENDING to be cleared.
> - Move inode sync operation into evict_inode from drop_inode.
> - Call upper_sb->sync_fs with no-wait after sync dirty upper
> inodes.
> - Hold s_inode_wblist_lock until deleting item from list.
> - Remove write_inode fuction because no more used.
>
> Changes since v4:
> - Add syncing operation and deleting from upper_inodes list
> during ovl inode destruction.
> - Export symbol of inode_wait_for_writeback() for waiting
> writeback on ovl inode.
> - Reuse I_SYNC flag to avoid race conditions between syncfs
> and drop_inode.
>
> Changes since v3:
> - Introduce upper_inode list to organize ovl inode which has upper
>   inode.
> - Avoid iput operation inside spin lock.
> - Change list iteration method for safety.
> - Reuse inode->i_wb_list and sb->s_inodes_wb to save memory.
> - Modify commit log and add more comments to the code.
>
> Changes since v2:
> - Decoupling with syncfs of upper fs by taking sb->s_sync_lock of
> overlayfs.
> - Factoring out sync operation to different helpers for easy
>   understanding.
>
> Changes since v1:
> - If upper filesystem is readonly mode then skip synchronization.
> - Introduce global wait list to replace temporary wait list for
> concurrent synchronization.
>
>  fs/overlayfs/Makefile    |   2 +-
>  fs/overlayfs/overlayfs.h |   9 ++
>  fs/overlayfs/ovl_entry.h |   5 +
>  fs/overlayfs/super.c     |  44 ++----
>  fs/overlayfs/sync.c      | 331 +++++++++++++++++++++++++++++++++++++++
>  fs/overlayfs/util.c      |  23 ++-
>  6 files changed, 381 insertions(+), 33 deletions(-)
>  create mode 100644 fs/overlayfs/sync.c
>
> diff --git a/fs/overlayfs/Makefile b/fs/overlayfs/Makefile
> index 9164c585eb2f..0c4e53fcf4ef 100644
> --- a/fs/overlayfs/Makefile
> +++ b/fs/overlayfs/Makefile
> @@ -6,4 +6,4 @@
>  obj-$(CONFIG_OVERLAY_FS) += overlay.o
>
>  overlay-objs := super.o namei.o util.o inode.o file.o dir.o readdir.o \
> -               copy_up.o export.o
> +               copy_up.o export.o sync.o
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 3623d28aa4fa..3cdb06e206a3 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -40,6 +40,10 @@ enum ovl_inode_flag {
>         OVL_UPPERDATA,
>         /* Inode number will remain constant over copy up. */
>         OVL_CONST_INO,
> +       /* Set when ovl inode is about to be freed */
> +       OVL_EVICT_PENDING,
> +       /* Set when sync upper inode in workqueue work */
> +       OVL_WRITE_INODE_PENDING,
>  };
>
>  enum ovl_entry_flag {
> @@ -295,6 +299,7 @@ bool ovl_is_metacopy_dentry(struct dentry *dentry);
>  char *ovl_get_redirect_xattr(struct dentry *dentry, int padding);
>  ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value,
>                      size_t padding);
> +void ovl_detach_upper_inodes_list(struct inode *inode);
>
>  static inline bool ovl_is_impuredir(struct dentry *dentry)
>  {
> @@ -466,3 +471,7 @@ int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
>
>  /* export.c */
>  extern const struct export_operations ovl_export_operations;
> +
> +/* sync.c */
> +void ovl_evict_inode(struct inode *inode);
> +int ovl_sync_fs(struct super_block *sb, int wait);
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 89015ea822e7..42e092e8cd61 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -75,6 +75,9 @@ struct ovl_fs {
>         struct inode *indexdir_trap;
>         /* -1: disabled, 0: same fs, 1..32: number of unused ino bits */
>         int xino_mode;
> +       /* Upper inode list and lock */
> +       spinlock_t upper_inodes_lock;
> +       struct list_head upper_inodes;
>  };
>
>  static inline struct ovl_fs *OVL_FS(struct super_block *sb)
> @@ -115,6 +118,8 @@ struct ovl_inode {
>
>         /* synchronize copy up and more */
>         struct mutex lock;
> +       /* Upper inodes list */
> +       struct list_head upper_inodes_list;
>  };
>
>  static inline struct ovl_inode *OVL_I(struct inode *inode)
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 319fe0d355b0..3e6871e1a7ba 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -183,6 +183,7 @@ static struct inode *ovl_alloc_inode(struct super_block *sb)
>         oi->lower = NULL;
>         oi->lowerdata = NULL;
>         mutex_init(&oi->lock);
> +       INIT_LIST_HEAD(&oi->upper_inodes_list);
>
>         return &oi->vfs_inode;
>  }
> @@ -249,36 +250,6 @@ static void ovl_put_super(struct super_block *sb)
>         ovl_free_fs(ofs);
>  }
>
> -/* Sync real dirty inodes in upper filesystem (if it exists) */
> -static int ovl_sync_fs(struct super_block *sb, int wait)
> -{
> -       struct ovl_fs *ofs = sb->s_fs_info;
> -       struct super_block *upper_sb;
> -       int ret;
> -
> -       if (!ofs->upper_mnt)
> -               return 0;
> -
> -       /*
> -        * If this is a sync(2) call or an emergency sync, all the super blocks
> -        * will be iterated, including upper_sb, so no need to do anything.
> -        *
> -        * If this is a syncfs(2) call, then we do need to call
> -        * sync_filesystem() on upper_sb, but enough if we do it when being
> -        * called with wait == 1.
> -        */
> -       if (!wait)
> -               return 0;
> -
> -       upper_sb = ofs->upper_mnt->mnt_sb;
> -
> -       down_read(&upper_sb->s_umount);
> -       ret = sync_filesystem(upper_sb);
> -       up_read(&upper_sb->s_umount);
> -
> -       return ret;
> -}
> -
>  /**
>   * ovl_statfs
>   * @sb: The overlayfs super block
> @@ -376,11 +347,19 @@ static int ovl_remount(struct super_block *sb, int *flags, char *data)
>         return 0;
>  }
>
> +static int ovl_drop_inode(struct inode *inode)
> +{
> +       if (ovl_inode_upper(inode))
> +               ovl_set_flag(OVL_EVICT_PENDING, inode);
> +       return 1;
> +}
> +
>  static const struct super_operations ovl_super_operations = {
>         .alloc_inode    = ovl_alloc_inode,
>         .free_inode     = ovl_free_inode,
>         .destroy_inode  = ovl_destroy_inode,
> -       .drop_inode     = generic_delete_inode,
> +       .drop_inode     = ovl_drop_inode,
> +       .evict_inode    = ovl_evict_inode,
>         .put_super      = ovl_put_super,
>         .sync_fs        = ovl_sync_fs,
>         .statfs         = ovl_statfs,
> @@ -1601,6 +1580,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
>         if (!ofs)
>                 goto out;
>
> +       spin_lock_init(&ofs->upper_inodes_lock);
> +       INIT_LIST_HEAD(&ofs->upper_inodes);
> +
>         ofs->creator_cred = cred = prepare_creds();
>         if (!cred)
>                 goto out_err;
> diff --git a/fs/overlayfs/sync.c b/fs/overlayfs/sync.c
> new file mode 100644
> index 000000000000..aecd312ec851
> --- /dev/null
> +++ b/fs/overlayfs/sync.c
> @@ -0,0 +1,331 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 All Rights Reserved.
> + * Author Chengguang Xu <cgxu519@mykernel.net>
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/xattr.h>
> +#include <linux/mount.h>
> +#include <linux/writeback.h>
> +#include <linux/blkdev.h>
> +#include "overlayfs.h"
> +
> +/**
> + * upper_inodes list is used for organizing potential target of syncfs,
> + * ovl inode which has upper inode will be added to this list while
> + * initializing or updating and will be deleted from this list while
> + * evicting.
> + *
> + * Introduce ovl_inode flag "OVL_EVICT_PENDING" to indicate the ovl inode
> + * is in eviction process, syncfs(actually ovl_sync_inodes()) will wait on
> + * evicting inode until the IO to be completed in evict_inode().
> + *
> + * inode state/ovl_inode flags cycle in syncfs context will be as below.
> + * OVL_EVICT_PENDING (ovl_inode->flags) is only marked when inode having
> + * upper inode.
> + *
> + * (allocation)
> + *   |
> + * I_NEW (inode->i_state)
> + *   |
> + * NONE  (inode->i_state)
> + *   |
> + * OVL_EVICT_PENDING (ovl_inode->flags)
> + *   |
> + * I_FREEING (inode->i_state) | OVL_EVICT_PENDING (ovl_inode->flags)
> + *   |
> + * I_FREEING (inode->i_state) | I_CLEAR (inode->i_state)
> + *   |
> + * (destruction)
> + *
> + *
> + * There are five locks in in syncfs contexts:
> + *
> + * upper_sb->s_umount(semaphore)    : avoiding r/o to r/w or vice versa
> + * sb->s_sync_lock(mutex)           : avoiding concorrent syncfs running
> + * ofs->upper_inodes_lock(spinlock) : protecting upper_inodes list
> + * sb->s_inode_wblist_lock(spinlock): protecting s_inodes_wb(sync waiting) list
> + * inode->i_lock(spinlock)          : protecting inode fields
> + *
> + * Lock dependencies in syncfs contexts:
> + *
> + * upper_sb->s_umount
> + *     sb->s_sync_lock
> + *             ofs->upper_inodes_lock
> + *                     inode->i_lock
> + *
> + * upper_sb->s_umount
> + *     sb->s_sync_lock
> + *             sb->s_inode_wblist_lock
> + *
> + */
> +
> +struct ovl_write_inode_work {
> +       struct work_struct work;
> +       struct inode *inode;
> +};
> +
> +static void ovl_write_inode_work_fn(struct work_struct *work)
> +{
> +       struct ovl_write_inode_work *ovl_wiw;
> +       struct inode *inode;
> +
> +       ovl_wiw = container_of(work, struct ovl_write_inode_work, work);
> +       inode = ovl_wiw->inode;
> +       write_inode_now(ovl_inode_upper(inode), 1);
> +
> +       spin_lock(&inode->i_lock);
> +       ovl_clear_flag(OVL_WRITE_INODE_PENDING, inode);
> +       wake_up_bit(&OVL_I(inode)->flags, OVL_WRITE_INODE_PENDING);
> +       spin_unlock(&inode->i_lock);
> +}
> +
> +void ovl_evict_inode(struct inode *inode)
> +{
> +       struct ovl_inode *oi = OVL_I(inode);
> +       struct ovl_write_inode_work ovl_wiw;
> +       DEFINE_WAIT_BIT(wait, &oi->flags, OVL_WRITE_INODE_PENDING);
> +       wait_queue_head_t *wqh;
> +
> +       if (ovl_inode_upper(inode)) {
> +               if (current->flags & PF_MEMALLOC) {
> +                       spin_lock(&inode->i_lock);
> +                       ovl_set_flag(OVL_WRITE_INODE_PENDING, inode);
> +                       wqh = bit_waitqueue(&oi->flags,
> +                                       OVL_WRITE_INODE_PENDING);
> +                       prepare_to_wait(wqh, &wait.wq_entry,
> +                                       TASK_UNINTERRUPTIBLE);
> +                       spin_unlock(&inode->i_lock);
> +
> +                       ovl_wiw.inode = inode;
> +                       INIT_WORK(&ovl_wiw.work, ovl_write_inode_work_fn);
> +                       schedule_work(&ovl_wiw.work);
> +
> +                       schedule();
> +                       finish_wait(wqh, &wait.wq_entry);

What is the reason to do this in another thread if this is a PF_MEMALLOC task?

> +               } else {
> +                       write_inode_now(ovl_inode_upper(inode), 1);
> +               }
> +               ovl_detach_upper_inodes_list(inode);
> +
> +               /*
> +                * ovl_sync_inodes() may wait until
> +                * flag OVL_EVICT_PENDING to be cleared.
> +                */
> +               spin_lock(&inode->i_lock);
> +               ovl_clear_flag(OVL_EVICT_PENDING, inode);
> +               wake_up_bit(&OVL_I(inode)->flags, OVL_EVICT_PENDING);
> +               spin_unlock(&inode->i_lock);
> +       }
> +       clear_inode(inode);
> +}
> +
> +void ovl_wait_evict_pending(struct inode *inode)
> +{
> +       struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> +       struct ovl_inode *oi = OVL_I(inode);
> +       DEFINE_WAIT_BIT(wait, &oi->flags, OVL_EVICT_PENDING);
> +       wait_queue_head_t *wqh;
> +
> +       wqh = bit_waitqueue(&oi->flags, OVL_EVICT_PENDING);
> +       prepare_to_wait(wqh, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
> +       spin_unlock(&inode->i_lock);
> +       spin_unlock(&ofs->upper_inodes_lock);
> +       schedule();
> +       finish_wait(wqh, &wait.wq_entry);
> +}
> +
> +/**
> + * ovl_sync_inodes
> + * @sb: The overlayfs super block
> + *
> + * upper_inodes list is used for organizing ovl inode which has upper inode,
> + * by iterating the list to looking for and syncing dirty upper inode.
> + *
> + * When starting syncing inode, we add the inode to wait list explicitly,
> + * in order to save memory we reuse inode->i_wb_list and sb->s_inodes_wb,
> + * so those fields have slightly differnt meanings in overlayfs.
> + */
> +static void ovl_sync_inodes(struct super_block *sb)
> +{
> +       struct ovl_fs *ofs = sb->s_fs_info;
> +       struct ovl_inode *oi;
> +       struct inode *inode;
> +       struct inode *upper_inode;
> +       struct blk_plug plug;
> +       LIST_HEAD(sync_tmp_list);
> +
> +       struct writeback_control wbc_for_sync = {
> +               .sync_mode              = WB_SYNC_ALL,
> +               .for_sync               = 1,
> +               .range_start            = 0,
> +               .range_end              = LLONG_MAX,
> +               .nr_to_write            = LONG_MAX,
> +       };
> +
> +       blk_start_plug(&plug);
> +       spin_lock(&ofs->upper_inodes_lock);
> +       list_splice_init(&ofs->upper_inodes, &sync_tmp_list);
> +
> +       while (!list_empty(&sync_tmp_list)) {
> +               oi = list_first_entry(&sync_tmp_list, struct ovl_inode,
> +                                               upper_inodes_list);
> +               inode = &oi->vfs_inode;
> +               spin_lock(&inode->i_lock);
> +
> +               if (inode->i_state & I_NEW) {
> +                       list_move_tail(&oi->upper_inodes_list,
> +                                       &ofs->upper_inodes);
> +                       spin_unlock(&inode->i_lock);
> +                       continue;
> +               }
> +
> +               /*
> +                * If ovl_inode flags is OVL_EVICT_PENDING,
> +                * left sync operation to the ovl_evict_inode(),
> +                * so wait here until OVL_EVICT_PENDING flag to be cleared.
> +                */
> +               if (ovl_test_flag(OVL_EVICT_PENDING, inode)) {
> +                       ovl_wait_evict_pending(inode);
> +                       goto next;

Does this skip re-adding to upper_inodes_list?

> +               }
> +
> +               list_move_tail(&oi->upper_inodes_list,
> +                               &ofs->upper_inodes);
> +               ihold(inode);
> +               upper_inode = ovl_inode_upper(inode);
> +               spin_unlock(&inode->i_lock);
> +               spin_unlock(&ofs->upper_inodes_lock);
> +
> +               if (!(upper_inode->i_state & I_DIRTY_ALL)) {
> +                       if (!mapping_tagged(upper_inode->i_mapping,
> +                                               PAGECACHE_TAG_WRITEBACK)) {
> +                               iput(inode);
> +                               goto next;
> +                       }
> +               } else {
> +                       sync_inode(upper_inode, &wbc_for_sync);
> +               }
> +
> +               spin_lock(&sb->s_inode_wblist_lock);
> +               list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
> +               spin_unlock(&sb->s_inode_wblist_lock);
> +
> +next:
> +               cond_resched();
> +               spin_lock(&ofs->upper_inodes_lock);
> +       }
> +       spin_unlock(&ofs->upper_inodes_lock);
> +       blk_finish_plug(&plug);
> +}
> +
> +/**
> + * ovl_wait_inodes
> + * @sb: The overlayfs super block
> + *
> + * Waiting writeback inodes which are in s_inodes_wb list,
> + * all the IO that has been issued up to the time this
> + * function is enter is guaranteed to be completed.
> + */
> +static void ovl_wait_inodes(struct super_block *sb)
> +{
> +       LIST_HEAD(sync_wait_list);
> +       struct inode *inode;
> +       struct inode *upper_inode;
> +
> +       /*
> +        * ovl inode in sb->s_inodes_wb list has already got inode reference,
> +        * this will avoid silent inode droping during waiting on it.
> +        *
> +        * Splice the sync wait list onto a temporary list to avoid waiting on
> +        * inodes that have started writeback after this point.
> +        */
> +       spin_lock(&sb->s_inode_wblist_lock);
> +       list_splice_init(&sb->s_inodes_wb, &sync_wait_list);
> +
> +       while (!list_empty(&sync_wait_list)) {
> +               inode = list_first_entry(&sync_wait_list, struct inode,
> +                                                       i_wb_list);
> +               list_del_init(&inode->i_wb_list);
> +               upper_inode = ovl_inode_upper(inode);
> +               spin_unlock(&sb->s_inode_wblist_lock);
> +
> +               if (!mapping_tagged(upper_inode->i_mapping,
> +                               PAGECACHE_TAG_WRITEBACK)) {
> +                       goto next;
> +               }
> +
> +               filemap_fdatawait_keep_errors(upper_inode->i_mapping);
> +               cond_resched();
> +
> +next:
> +               iput(inode);
> +               spin_lock(&sb->s_inode_wblist_lock);
> +       }
> +       spin_unlock(&sb->s_inode_wblist_lock);
> +}
> +
> +/**
> + * ovl_sync_filesystem
> + * @sb: The overlayfs super block
> + *
> + * Sync underlying dirty inodes in upper filesystem and
> + * wait for completion.
> + */
> +static int ovl_sync_filesystem(struct super_block *sb)
> +{
> +       struct ovl_fs *ofs = sb->s_fs_info;
> +       struct super_block *upper_sb = ofs->upper_mnt->mnt_sb;
> +       int ret = 0;
> +
> +       down_read(&upper_sb->s_umount);
> +       if (!sb_rdonly(upper_sb)) {
> +               /*
> +                * s_sync_lock is used for serializing concurrent
> +                * syncfs operations.
> +                */
> +               mutex_lock(&sb->s_sync_lock);
> +               ovl_sync_inodes(sb);
> +               /* Calling sync_fs with no-wait for better performance. */
> +               if (upper_sb->s_op->sync_fs)
> +                       upper_sb->s_op->sync_fs(upper_sb, 0);
> +
> +               ovl_wait_inodes(sb);
> +               if (upper_sb->s_op->sync_fs)
> +                       upper_sb->s_op->sync_fs(upper_sb, 1);
> +
> +               ret = sync_blockdev(upper_sb->s_bdev);
> +               mutex_unlock(&sb->s_sync_lock);
> +       }
> +       up_read(&upper_sb->s_umount);
> +       return ret;
> +}
> +
> +/**
> + * ovl_sync_fs
> + * @sb: The overlayfs super block
> + * @wait: Wait for I/O to complete
> + *
> + * Sync real dirty inodes in upper filesystem (if it exists)
> + */
> +int ovl_sync_fs(struct super_block *sb, int wait)
> +{
> +       struct ovl_fs *ofs = sb->s_fs_info;
> +
> +       if (!ofs->upper_mnt)
> +               return 0;
> +
> +       /*
> +        * If this is a sync(2) call or an emergency sync, all the super blocks
> +        * will be iterated, including upper_sb, so no need to do anything.
> +        *
> +        * If this is a syncfs(2) call, then we do need to call
> +        * sync_filesystem() on upper_sb, but enough if we do it when being
> +        * called with wait == 1.
> +        */
> +       if (!wait)
> +               return 0;
> +
> +       return ovl_sync_filesystem(sb);
> +}
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index ea005085803f..73ef195d9aef 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -386,13 +386,33 @@ void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect)
>         oi->redirect = redirect;
>  }
>
> +void ovl_attach_upper_inodes_list(struct inode *inode)
> +{
> +       struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> +
> +       spin_lock(&ofs->upper_inodes_lock);
> +       list_add(&OVL_I(inode)->upper_inodes_list, &ofs->upper_inodes);
> +       spin_unlock(&ofs->upper_inodes_lock);
> +}
> +
> +void ovl_detach_upper_inodes_list(struct inode *inode)
> +{
> +       struct ovl_fs *ofs = inode->i_sb->s_fs_info;
> +
> +       spin_lock(&ofs->upper_inodes_lock);
> +       list_del_init(&OVL_I(inode)->upper_inodes_list);
> +       spin_unlock(&ofs->upper_inodes_lock);
> +}
> +
>  void ovl_inode_init(struct inode *inode, struct dentry *upperdentry,
>                     struct dentry *lowerdentry, struct dentry *lowerdata)
>  {
>         struct inode *realinode = d_inode(upperdentry ?: lowerdentry);
>
> -       if (upperdentry)
> +       if (upperdentry) {
>                 OVL_I(inode)->__upperdentry = upperdentry;
> +               ovl_attach_upper_inodes_list(inode);
> +       }
>         if (lowerdentry)
>                 OVL_I(inode)->lower = igrab(d_inode(lowerdentry));
>         if (lowerdata)
> @@ -421,6 +441,7 @@ void ovl_inode_update(struct inode *inode, struct dentry *upperdentry)
>                 inode->i_private = upperinode;
>                 __insert_inode_hash(inode, (unsigned long) upperinode);
>         }
> +       ovl_attach_upper_inodes_list(inode);
>  }
>
>  static void ovl_dentry_version_inc(struct dentry *dentry, bool impurity)
> --
> 2.21.1
>
>
>