On Mon, 2016-08-22 at 10:54 +0200, Hannes Reinecke wrote:
> When shutting down a session I'm seeing this hung_task message:
>
> INFO: task kworker/u128:0:6 blocked for more than 480 seconds.
> Tainted: G E N 4.4.17-default+ #241
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> kworker/u128:0 D ffff880237615c00 0 6 2 0x00000000
> Workqueue: fc_rport_eq fc_rport_work [libfc]
> ffff88017edd7c48 ffffffff81c11500 ffff88017edd0180 ffff88017edd8000
> ffff88035b6860a8 ffff88017edd0180 ffff88036461eac0 0000000000000000
> ffff88017edd7c60 ffffffff815db4d5 7fffffffffffffff ffff88017edd7d10
> Call Trace:
> [<ffffffff815db4d5>] schedule+0x35/0x80
> [<ffffffff815dde17>] schedule_timeout+0x237/0x2d0
> [<ffffffff815dc6e3>] wait_for_completion+0xa3/0x110
> [<ffffffffa0869fb5>] target_wait_for_sess_cmds+0x45/0x190 [target_core_mod]
> [<ffffffffa03953b4>] ft_close_sess+0x24/0x30 [tcm_fc]
> [<ffffffffa03955ba>] ft_prlo+0x8a/0x95 [tcm_fc]
> [<ffffffffa066fc28>] fc_rport_work+0x3b8/0x7c0 [libfc]
> [<ffffffff810939ee>] process_one_work+0x14e/0x410
> [<ffffffff81094246>] worker_thread+0x116/0x490
>
> Looking at the code it looks as if there is some confusion about
> when to call 'wait_for_completion(&cmd->cmd_wait_comp).
> The problem is that there are _two_ sections where the code
> waits for 'cmd_wait_comp' completion, but the completion
> is only called with 'complete', not 'complete_all'.
> So we cannot have both waiting for it, doing so will lead
> to a stuck wait_for_completion.
>
> Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
> ---
> drivers/target/target_core_transport.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 6094a6b..2e1a6d8 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -2522,7 +2522,7 @@ int transport_generic_free_cmd(struct se_cmd *cmd, int wait_for_tasks)
> * the remaining calls to target_put_sess_cmd(), and not the
> * callers of this function.
> */
> - if (aborted) {
> + if (aborted && !cmd->cmd_wait_set) {
> pr_debug("Detected CMD_T_ABORTED for ITT: %llu\n", cmd->tag);
> wait_for_completion(&cmd->cmd_wait_comp);
> cmd->se_tfo->release_cmd(cmd);
Do you recall if hung se_cmd shutdown was with both CMD_T_ABORTED and
!CMD_T_ABORTED descriptors, or former only..?
Using v4.4.y code for CMD_T_ABORTED, you likely hit the missing
SCF_ACK_KREF assignment regression leak:
http://www.spinics.net/lists/target-devel/msg13530.html
> @@ -2642,9 +2642,11 @@ void target_sess_cmd_list_set_waiting(struct se_session *se_sess)
> list_for_each_entry(se_cmd, &se_sess->sess_wait_list, se_cmd_list) {
> rc = kref_get_unless_zero(&se_cmd->cmd_kref);
> if (rc) {
> - se_cmd->cmd_wait_set = 1;
> spin_lock(&se_cmd->t_state_lock);
> - se_cmd->transport_state |= CMD_T_FABRIC_STOP;
> + if (!(se_cmd->transport_state & CMD_T_FABRIC_STOP)) {
> + se_cmd->cmd_wait_set = 1;
> + se_cmd->transport_state |= CMD_T_FABRIC_STOP;
> + }
> spin_unlock(&se_cmd->t_state_lock);
> }
> }
So tcm_fc uses transport_generic_free_cmd(se_cmd, wait_for_tasks=0) in
ft_check_stop_free() to drop the extra SCF_ACK_KREF reference, which
does the extra if (aborted) check + possible sleep mentioned above.
AFAICT, ft_check_stop_free() response callback should be using
target_put_sess_cmd() to drop se_cmd->cmd_kref, and not attempt to block
for aborted status at all..
> @@ -2664,24 +2666,26 @@ void target_wait_for_sess_cmds(struct se_session *se_sess)
>
> list_for_each_entry_safe(se_cmd, tmp_cmd,
> &se_sess->sess_wait_list, se_cmd_list) {
> + int cmd_wait;
> pr_debug("Waiting for se_cmd: %p t_state: %d, fabric state:"
> " %d\n", se_cmd, se_cmd->t_state,
> se_cmd->se_tfo->get_cmd_state(se_cmd));
>
> spin_lock_irqsave(&se_cmd->t_state_lock, flags);
> tas = (se_cmd->transport_state & CMD_T_TAS);
> + cmd_wait = se_cmd->cmd_wait_set;
> spin_unlock_irqrestore(&se_cmd->t_state_lock, flags);
> -
> if (!target_put_sess_cmd(se_cmd)) {
> if (tas)
> target_put_sess_cmd(se_cmd);
> }
> -
> + if (!cmd_wait)
> + continue;
> wait_for_completion(&se_cmd->cmd_wait_comp);
> pr_debug("After cmd_wait_comp: se_cmd: %p t_state: %d"
> " fabric state: %d\n", se_cmd, se_cmd->t_state,
> se_cmd->se_tfo->get_cmd_state(se_cmd));
> -
> + se_cmd->cmd_wait_set = 0;
> se_cmd->se_tfo->release_cmd(se_cmd);
> }
>
target_wait_for_sess_cmd() must always wait for se_cmd->cmd_wait_comp to
finish, because fabric drivers currently expect all outstanding
se_cmd->se_sess to complete before it's safe to release driver specific
session resources.
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