On Mon, 2016-08-22 at 10:54 +0200, Hannes Reinecke wrote:
> target_sess_cmd_list_waiting() might hit on a condition where
> the kref for the command is already 0, but the destructor has
> not been called yet (or is stuck in waiting for a spin lock).
> Rather than leaving the command on the list we should explicitly
> remove it to avoid race issues later on.
>
> Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
> ---
> drivers/target/target_core_transport.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 2e1a6d8..ce136f0 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -2547,8 +2547,8 @@ int target_get_sess_cmd(struct se_cmd *se_cmd, bool ack_kref)
> * fabric acknowledgement that requires two target_put_sess_cmd()
> * invocations before se_cmd descriptor release.
> */
> - if (ack_kref)
> - kref_get(&se_cmd->cmd_kref);
> + if (ack_kref && !kref_get_unless_zero(&se_cmd->cmd_kref))
> + return -EINVAL;
>
Makes sense.
Applying the following version to target-pending/master atop pending
SCF_ACK_KREF regression bug-fix.
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 9ebbf94..ad6fb3f 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2535,7 +2535,9 @@ int target_get_sess_cmd(struct se_cmd *se_cmd, bool ack_kref)
* invocations before se_cmd descriptor release.
*/
if (ack_kref) {
- kref_get(&se_cmd->cmd_kref);
+ if (!kref_get_unless_zero(&se_cmd->cmd_kref))
+ return -EINVAL;
+
se_cmd->se_cmd_flags |= SCF_ACK_KREF;
}
> spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
> if (se_sess->sess_tearing_down) {
> @@ -2627,7 +2627,7 @@ EXPORT_SYMBOL(target_put_sess_cmd);
> */
> void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
> {
> - struct se_cmd *se_cmd;
> + struct se_cmd *se_cmd, *tmp_cmd;
> unsigned long flags;
> int rc;
>
> @@ -2639,7 +2639,8 @@ void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
> se_sess->sess_tearing_down = 1;
> list_splice_init(&se_sess->sess_cmd_list, &se_sess->sess_wait_list);
>
> - list_for_each_entry(se_cmd, &se_sess->sess_wait_list, se_cmd_list) {
> + list_for_each_entry_safe(se_cmd, tmp_cmd,
> + &se_sess->sess_wait_list, se_cmd_list) {
> rc = kref_get_unless_zero(&se_cmd->cmd_kref);
> if (rc) {
> spin_lock(&se_cmd->t_state_lock);
> @@ -2648,7 +2649,8 @@ void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
> se_cmd->transport_state |= CMD_T_FABRIC_STOP;
> }
> spin_unlock(&se_cmd->t_state_lock);
> - }
> + } else
> + list_del_init(&se_cmd->se_cmd_list);
> }
>
> spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
--
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