linux-kernel - RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from atomic_t to refcount

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Date:   Wed, 22 Feb 2017 11:17:20 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        "Kees Cook" <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: RE: [PATCH 1/7] fs, xfs: convert xfs_bui_log_item.bui_refcount from
 atomic_t to refcount_t

> On Tue, Feb 21, 2017 at 05:49:01PM +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.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> > Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: David Windsor <dwindsor@...il.com>
> > ---
> >  fs/xfs/xfs_bmap_item.c | 4 ++--
> >  fs/xfs/xfs_bmap_item.h | 4 +++-
> >  2 files changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> > index 9bf57c7..33104ad 100644
> > --- a/fs/xfs/xfs_bmap_item.c
> > +++ b/fs/xfs/xfs_bmap_item.c
> > @@ -199,7 +199,7 @@ xfs_bui_init(
> >  	buip->bui_format.bui_nextents =
> XFS_BUI_MAX_FAST_EXTENTS;
> >  	buip->bui_format.bui_id = (uintptr_t)(void *)buip;
> >  	atomic_set(&buip->bui_next_extent, 0);
> > -	atomic_set(&buip->bui_refcount, 2);
> > +	refcount_set(&buip->bui_refcount, 2);
> >
> >  	return buip;
> >  }
> > @@ -215,7 +215,7 @@ void
> >  xfs_bui_release(
> >  	struct xfs_bui_log_item	*buip)
> >  {
> > -	if (atomic_dec_and_test(&buip->bui_refcount)) {
> > +	if (refcount_dec_and_test(&buip->bui_refcount)) {
> >  		xfs_trans_ail_remove(&buip->bui_item,
> SHUTDOWN_LOG_IO_ERROR);
> >  		xfs_bui_item_free(buip);
> >  	}
> > diff --git a/fs/xfs/xfs_bmap_item.h b/fs/xfs/xfs_bmap_item.h
> > index c867daa..988a6ae 100644
> > --- a/fs/xfs/xfs_bmap_item.h
> > +++ b/fs/xfs/xfs_bmap_item.h
> > @@ -20,6 +20,8 @@
> >  #ifndef	__XFS_BMAP_ITEM_H__
> >  #define	__XFS_BMAP_ITEM_H__
> >
> > +#include <linux/refcount.h>
> 
> Seeing as you're sprinkling refcount_t all over XFS, this ought to go in
> xfs_linux.h with all the other Linux-specific #includes.
> 
> --D

Sure, I will move the include there and leave only one. 
Will send a next version also after fixing the other non-reference counters case we discussed. 

Best Regards,
Elena.
> 
> > +
> >  /*
> >   * There are (currently) two pairs of bmap btree redo item types: map &
> unmap.
> >   * The common abbreviations for these are BUI (bmap update intent) and
> BUD
> > @@ -61,7 +63,7 @@ struct kmem_zone;
> >   */
> >  struct xfs_bui_log_item {
> >  	struct xfs_log_item		bui_item;
> > -	atomic_t			bui_refcount;
> > +	refcount_t			bui_refcount;
> >  	atomic_t			bui_next_extent;
> >  	unsigned long			bui_flags;	/* misc
> flags */
> >  	struct xfs_bui_log_format	bui_format;
> > --
> > 2.7.4
> >
> > --
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