linux-kernel - RE: [f2fs-dev] [PATCH 08/12] f2fs: introduce a shrinker for mounted fs

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Date:	Thu, 2 Jul 2015 20:32:39 +0800
From:	Chao Yu <yuchaochina@...mail.com>
To:	"'Jaegeuk Kim'" <jaegeuk@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-f2fs-devel@...ts.sourceforge.net>
Subject: RE: [f2fs-dev] [PATCH 08/12] f2fs: introduce a shrinker for mounted fs

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Tuesday, June 30, 2015 2:40 AM
> To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> linux-f2fs-devel@...ts.sourceforge.net
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 08/12] f2fs: introduce a shrinker for mounted fs
> 
> This patch introduces a shrinker targeting to reduce memory footprint consumed
> by a number of in-memory f2fs data structures.
> 
> In addition, it newly adds:
>  - sbi->umount_mutex to avoid data races on shrinker and put_super
>  - sbi->shruinker_run_no to not revisit objects
> 
> Noteh that the basic implementation was copied from fs/btrfs/shrinker.c

This file seems not exist...

> @@ -1310,6 +1328,7 @@ free_root_inode:
>  	dput(sb->s_root);
>  	sb->s_root = NULL;
>  free_node_inode:
> +	f2fs_leave_shrinker(sbi);

We should detach shrinker under sbi->umount_mutex.
Otherwise we will access freed memory in following call path:

mount					shrinker
->fill_super
  Failed after f2fs_join_shrinker
  ->f2fs_leave_shrinker
					->f2fs_shrink_scan
					  spin_lock
					  get sbi pointer
					  spin_unlock
    spin_lock
    list_del sbi->s_list
    spin_unlock
    free sbi
					  use-after-free for sbi

Thanks,
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