Re: [f2fs-dev] [PATCH] f2fs: reposition unlock_new_inode to prevent accessing invalid inode

[Changman Lee <cm224.lee@samsung.com>]

Hi,

On Thu, Aug 28, 2014 at 04:53:01PM +0800, Chao Yu wrote:
> Hi Changman,
> 
> > -----Original Message-----
> > From: Changman Lee [mailto:cm224.lee@samsung.com]
> > Sent: Thursday, August 28, 2014 9:48 AM
> > To: Chao Yu
> > Cc: Jaegeuk Kim; linux-kernel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net
> > Subject: Re: [f2fs-dev] [PATCH] f2fs: reposition unlock_new_inode to prevent accessing invalid
> > inode
> > 
> > Hi Chao,
> > 
> > I agree it's correct unlock_new_inode should be located after make_bad_inode.
> > 
> > About this scenario,
> > I think we should check some condition if this could be occured;
> 
> I think this condition is the almost impossible but which can happen theoretically.
> 
> > A inode allocated newly could be victim by gc thread.
> > Then, f2fs_iget called by Thread A have to fail because we handled it as
> > bad_inode in Thread B. However, f2fs_iget could still get inode.
> > How about check it using is_bad_inode() in f2fs_iget.
> 
> Yes, agreed. How about return -EIO when this inode we iget_locked is bad?

Hmm.. It might be better to check return value of f2fs_iget like other f/s.

- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -595,6 +595,8 @@ next_step:
                        inode = f2fs_iget(sb, dni.ino);
                        if (IS_ERR(inode))
                                continue;
+                       else if (is_bad_inode(inode))
+                               continue;


Thanks,
Changman

> 
> Thanks,
> Yu
> 
> > 
> > Thanks,
> > 
> > On Tue, Aug 26, 2014 at 06:35:29PM +0800, Chao Yu wrote:
> > > As the race condition on the inode cache, following scenario can appear:
> > > [Thread a]				[Thread b]
> > > 					->f2fs_mkdir
> > > 					  ->f2fs_add_link
> > > 					    ->__f2fs_add_link
> > > 					      ->init_inode_metadata failed here
> > > ->gc_thread_func
> > >   ->f2fs_gc
> > >     ->do_garbage_collect
> > >       ->gc_data_segment
> > >         ->f2fs_iget
> > >           ->iget_locked
> > >             ->wait_on_inode
> > > 					  ->unlock_new_inode
> > >         ->move_data_page
> > > 					  ->make_bad_inode
> > > 					  ->iput
> > >
> > > When we fail in create/symlink/mkdir/mknod/tmpfile, the new allocated inode
> > > should be set as bad to avoid being accessed by other thread. But in above
> > > scenario, it allows f2fs to access the invalid inode before this inode was set
> > > as bad.
> > > This patch fix the potential problem, and this issue was found by code review.
> > >
> > > Signed-off-by: Chao Yu <chao2.yu@samsung.com>
> > > ---
> > >  fs/f2fs/namei.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> > > index 6b53ce9..845f1be 100644
> > > --- a/fs/f2fs/namei.c
> > > +++ b/fs/f2fs/namei.c
> > > @@ -134,8 +134,8 @@ static int f2fs_create(struct inode *dir, struct dentry *dentry, umode_t
> > mode,
> > >  	return 0;
> > >  out:
> > >  	clear_nlink(inode);
> > > -	unlock_new_inode(inode);
> > >  	make_bad_inode(inode);
> > > +	unlock_new_inode(inode);
> > >  	iput(inode);
> > >  	alloc_nid_failed(sbi, ino);
> > >  	return err;
> > > @@ -267,8 +267,8 @@ static int f2fs_symlink(struct inode *dir, struct dentry *dentry,
> > >  	return err;
> > >  out:
> > >  	clear_nlink(inode);
> > > -	unlock_new_inode(inode);
> > >  	make_bad_inode(inode);
> > > +	unlock_new_inode(inode);
> > >  	iput(inode);
> > >  	alloc_nid_failed(sbi, inode->i_ino);
> > >  	return err;
> > > @@ -308,8 +308,8 @@ static int f2fs_mkdir(struct inode *dir, struct dentry *dentry, umode_t
> > mode)
> > >  out_fail:
> > >  	clear_inode_flag(F2FS_I(inode), FI_INC_LINK);
> > >  	clear_nlink(inode);
> > > -	unlock_new_inode(inode);
> > >  	make_bad_inode(inode);
> > > +	unlock_new_inode(inode);
> > >  	iput(inode);
> > >  	alloc_nid_failed(sbi, inode->i_ino);
> > >  	return err;
> > > @@ -354,8 +354,8 @@ static int f2fs_mknod(struct inode *dir, struct dentry *dentry,
> > >  	return 0;
> > >  out:
> > >  	clear_nlink(inode);
> > > -	unlock_new_inode(inode);
> > >  	make_bad_inode(inode);
> > > +	unlock_new_inode(inode);
> > >  	iput(inode);
> > >  	alloc_nid_failed(sbi, inode->i_ino);
> > >  	return err;
> > > @@ -688,8 +688,8 @@ release_out:
> > >  out:
> > >  	f2fs_unlock_op(sbi);
> > >  	clear_nlink(inode);
> > > -	unlock_new_inode(inode);
> > >  	make_bad_inode(inode);
> > > +	unlock_new_inode(inode);
> > >  	iput(inode);
> > >  	alloc_nid_failed(sbi, inode->i_ino);
> > >  	return err;
> > > --
> > > 2.0.0.421.g786a89d
> > >
> > >
> > >
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