On Sat, Jul 17, 2021 at 06:21:02PM +0800, Xiyu Yang wrote:
> refcount_t type and corresponding API can protect refcounters from
> accidental underflow and overflow and further use-after-free situations.
>
> Signed-off-by: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
> Signed-off-by: Xin Tan <tanxin.ctf@xxxxxxxxx>
> ---
> fs/xfs/xfs_log.c | 10 +++++-----
> fs/xfs/xfs_log_priv.h | 4 +++-
> 2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 36fa2650b081..1da711f1a229 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -3347,8 +3347,8 @@ void
> xfs_log_ticket_put(
> xlog_ticket_t *ticket)
> {
> - ASSERT(atomic_read(&ticket->t_ref) > 0);
> - if (atomic_dec_and_test(&ticket->t_ref))
> + ASSERT(refcount_read(&ticket->t_ref) > 0);
> + if (refcount_dec_and_test(&ticket->t_ref))
I thought the refcount functions already had code to warn about
refcounts that get decremented below zero...
> kmem_cache_free(xfs_log_ticket_zone, ticket);
> }
>
> @@ -3356,8 +3356,8 @@ xlog_ticket_t *
> xfs_log_ticket_get(
> xlog_ticket_t *ticket)
> {
> - ASSERT(atomic_read(&ticket->t_ref) > 0);
> - atomic_inc(&ticket->t_ref);
> + ASSERT(refcount_read(&ticket->t_ref) > 0);
...and can't come back from the dead? Also, how much of a performance
impact does this have over the atomic_t functions? The last time anyone
proposed conversions similar to this, there were concerns about that.
--D
> + refcount_inc(&ticket->t_ref);
> return ticket;
> }
>
> @@ -3477,7 +3477,7 @@ xlog_ticket_alloc(
>
> unit_res = xlog_calc_unit_res(log, unit_bytes);
>
> - atomic_set(&tic->t_ref, 1);
> + refcount_set(&tic->t_ref, 1);
> tic->t_task = current;
> INIT_LIST_HEAD(&tic->t_queue);
> tic->t_unit_res = unit_res;
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index 4c41bbfa33b0..c4157d87cea4 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -6,6 +6,8 @@
> #ifndef __XFS_LOG_PRIV_H__
> #define __XFS_LOG_PRIV_H__
>
> +#include <linux/refcount.h>
> +
> struct xfs_buf;
> struct xlog;
> struct xlog_ticket;
> @@ -163,7 +165,7 @@ typedef struct xlog_ticket {
> struct list_head t_queue; /* reserve/write queue */
> struct task_struct *t_task; /* task that owns this ticket */
> xlog_tid_t t_tid; /* transaction identifier : 4 */
> - atomic_t t_ref; /* ticket reference count : 4 */
> + refcount_t t_ref; /* ticket reference count : 4 */
> int t_curr_res; /* current reservation in bytes : 4 */
> int t_unit_res; /* unit reservation in bytes : 4 */
> char t_ocnt; /* original count : 1 */
> --
> 2.7.4
>
