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Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from atomic_t to refcount_t

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On Tue, Feb 21, 2017 at 04:06:30PM +0000, Reshetova, Elena wrote:
> > On Tue, Feb 21, 2017 at 05:49:03PM +0200, Elena Reshetova wrote:
> > > refcount_t type and corresponding API should be
> > > used instead of atomic_t when the variable is used as
> > > a reference counter. This allows to avoid accidental
> > > refcounter overflows that might lead to use-after-free
> > > situations.
> > 
> > Changelog forgets to mention if this was runtime tested..
> 
> It was boot-tested in the whole refcount_t changes pile, which is not very useful for fs anyway. 
> What's why we are sending this through maintainers to get through their tests. 
> I am sure that testing would be better than what we can do. 

For FS changes, I would recommend at the very least running xfstests on
an instance (which unlike the name suggests is good for most block
filesystems Linux has).

> > > @@ -432,7 +432,7 @@ xfs_trans_brelse(xfs_trans_t	*tp,
> > >  /***
> > >  		ASSERT(bp->b_pincount == 0);
> > >  ***/
> > > -		ASSERT(atomic_read(&bip->bli_refcount) == 0);
> > > +		ASSERT(refcount_read(&bip->bli_refcount) == 0);
> > >  		ASSERT(!(bip->bli_item.li_flags & XFS_LI_IN_AIL));
> > >  		ASSERT(!(bip->bli_flags & XFS_BLI_INODE_ALLOC_BUF));
> > >  		xfs_buf_item_relse(bp);
> > 
> > 
> > This for example looks dodgy.
> > 
> > That seems to suggest the atomic_dec() there can actually hit 0, which
> > _will_ generate a WARN.
> 
> True, but in some of this cases WARN might be ok, I think? As soon as
> functionality is not changed and object is not reused (by doing
> refcount_inc on it) anywhere later on. 

No, your conversion should not generate spurious WARN()s.

And also no, atomic_dec() must not hit 0. If you've been _that_ careful
with your reference counting and you absolutely _know_ this is the very
last one, write something like:

  WARN_ON(!refcount_dec_if_one());


Please, stop sending out conversions that haven't been tested. And take
the time to actually look at your own patches. If I can spot fail just
looking through them, so can you (or any of the other many people in
your SoB chain).

Take a little more time and a little extra care.

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[PATCH 0/7] fs, xfs subsystem refcounter conversions Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 16:50 +0100
  [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 16:50 +0100
    Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-02-21 17:40 +0100
      RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:20 +0100
    Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t Dave Chinner <david@fromorbit.com> - 2017-02-22 00:00 +0100
      RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:30 +0100
        Re: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t Dave Chinner <david@fromorbit.com> - 2017-02-22 23:10 +0100
          RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-23 09:00 +0100
  [PATCH 5/7] fs, xfs: convert xlog_ticket.t_ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:00 +0100
    RE: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-21 17:10 +0100
      Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:30 +0100
        Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:40 +0100
      Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t "Darrick J. Wong" <darrick.wong@oracle.com> - 2017-02-21 18:10 +0100
        Re: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t Brian Foster <bfoster@redhat.com> - 2017-02-21 20:30 +0100
          RE: [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from  atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:30 +0100
  [PATCH 7/7] fs, xfs: convert xfs_rui_log_item.rui_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  [PATCH 4/7] fs, xfs: convert xfs_efi_log_item.efi_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  [PATCH 3/7] fs, xfs: convert xfs_buf_log_item.bli_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
  [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and xfs_buf.b_lru_ref from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100
    Re: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and  xfs_buf.b_lru_ref from atomic_t to refcount_t Peter Zijlstra <peterz@infradead.org> - 2017-02-21 17:10 +0100
      Re: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and  xfs_buf.b_lru_ref from atomic_t to refcount_t Dave Chinner <david@fromorbit.com> - 2017-02-22 00:00 +0100
        RE: [PATCH 2/7] fs, xfs: convert xfs_buf.b_hold and  xfs_buf.b_lru_ref from atomic_t to refcount_t "Reshetova, Elena" <elena.reshetova@intel.com> - 2017-02-22 12:20 +0100
  [PATCH 6/7] fs, xfs: convert xfs_cui_log_item.cui_refcount from atomic_t to refcount_t Elena Reshetova <elena.reshetova@intel.com> - 2017-02-21 17:00 +0100

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