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

[Chao Yu]

Hi Changman,

> -----Original Message-----
> From: Changman Lee [mailto:cm224.lee@xxxxxxxxxxx]
> Sent: Thursday, August 28, 2014 9:48 AM
> To: Chao Yu
> Cc: Jaegeuk Kim; linux-kernel@xxxxxxxxxxxxxxx; linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> 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?

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@xxxxxxxxxxx>
> > ---
> >  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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> > _______________________________________________
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