linux-kernel - Re: [PATCH v2 05/17] locks: generic_delete_lease doesn't need a file

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Message-ID: <20150113120343.02e0b977@notabene.brown>
Date:	Tue, 13 Jan 2015 12:03:43 +1300
From:	NeilBrown <neilb@...e.de>
To:	Jeff Layton <jlayton@...marydata.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-kernel@...r.kernel.org, "L. A. Walsh" <suse@...nx.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH v2 05/17] locks: generic_delete_lease doesn't need a
 file_lock at all

On Thu,  4 Sep 2014 08:38:31 -0400 Jeff Layton <jlayton@...marydata.com>
wrote:

> Ensure that it's OK to pass in a NULL file_lock double pointer on
> a F_UNLCK request and convert the vfs_setlease F_UNLCK callers to
> do just that.
> 
> Finally, turn the BUG_ON in generic_setlease into a WARN_ON_ONCE
> with an error return. That's a problem we can handle without
> crashing the box if it occurs.
> 
> Signed-off-by: Jeff Layton <jlayton@...marydata.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> ---
>  fs/locks.c                      | 34 ++++++++++++++--------------------
>  fs/nfsd/nfs4state.c             |  2 +-
>  include/trace/events/filelock.h | 14 +++++++-------
>  3 files changed, 22 insertions(+), 28 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 4031324e6cca..1289b74fffbf 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -1637,22 +1637,23 @@ out:
>  	return error;
>  }
>  
> -static int generic_delete_lease(struct file *filp, struct file_lock **flp)
> +static int generic_delete_lease(struct file *filp)
>  {
> +	int error = -EAGAIN;
>  	struct file_lock *fl, **before;
>  	struct dentry *dentry = filp->f_path.dentry;
>  	struct inode *inode = dentry->d_inode;
>  
> -	trace_generic_delete_lease(inode, *flp);
> -
>  	for (before = &inode->i_flock;
>  			((fl = *before) != NULL) && IS_LEASE(fl);
>  			before = &fl->fl_next) {
> -		if (fl->fl_file != filp)
> -			continue;
> -		return (*flp)->fl_lmops->lm_change(before, F_UNLCK);
> +		if (fl->fl_file == filp)
> +			break;
>  	}
> -	return -EAGAIN;
> +	trace_generic_delete_lease(inode, fl);
> +	if (fl)
> +		error = fl->fl_lmops->lm_change(before, F_UNLCK);
> +	return error;
>  }

Hi Jeff,
 I have a report of a crash in 3.18 because fl->fl_lmops is NULL in the above.
   https://bugzilla.suse.com/show_bug.cgi?id=912569

I assume this happens because a file_lock is found which is not IS_LEASE.
When that happens, the loop will abort, but fl will not be NULL.
As non-LEASE locks have  a NULL fl_lmops, we crash.

I would be inclined to put the code back the way it was, and just move the
trace_generic_delete_lease call.

Alternately we could make it

  if (fl && IS_LEASE(fl))
          error = fl->fl_lmops-> .....

What do you think?

NeilBrown

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