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

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Date:	Fri, 3 Jul 2015 21:51:58 -0700
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <yuchaochina@...mail.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 08/12] f2fs: introduce a shrinker for mounted
 fs

On Thu, Jul 02, 2015 at 08:32:39PM +0800, Chao Yu wrote:
> > -----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

Right, confirmed this.

Thanks,

> 
> Thanks,
> 
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