Re: [PATCH v2 05/17] locks: generic_delete_lease doesn't need a file_lock at all

NeilBrown
2015-01-12T23:04:11Z

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On Thu, 4 Sep 2014 08:38:31 -0400 Jeff Layton <jlayton@primarydata.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@primarydata.com>
> Reviewed-by: Christoph Hellwig <hch@lst.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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