Re: [PATCH v2] IB/iser: Remove in_interrupt() usage.

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Dec 04, 2020 at 06:42:56PM +0100, Sebastian Andrzej Siewior wrote:
> iser_initialize_task_headers() uses in_interrupt() to find out if it is
> safe to acquire a mutex.
> 
> in_interrupt() is deprecated as it is ill defined and does not provide what
> it suggests. Aside of that it covers only parts of the contexts in which
> a mutex may not be acquired.
> 
> The following callchains exist:
> 
> iscsi_queuecommand() *locks* iscsi_session::frwd_lock
> -> iscsi_prep_scsi_cmd_pdu()
>    -> session->tt->init_task() (iscsi_iser_task_init())
>       -> iser_initialize_task_headers()
> -> iscsi_iser_task_xmit() (iscsi_transport::xmit_task)
>   -> iscsi_iser_task_xmit_unsol_data()
>     -> iser_send_data_out()
>       -> iser_initialize_task_headers()
> 
> iscsi_data_xmit() *locks* iscsi_session::frwd_lock
> -> iscsi_prep_mgmt_task()
>    -> session->tt->init_task() (iscsi_iser_task_init())
>       -> iser_initialize_task_headers()
> -> iscsi_prep_scsi_cmd_pdu()
>    -> session->tt->init_task() (iscsi_iser_task_init())
>       -> iser_initialize_task_headers()
> 
> __iscsi_conn_send_pdu() caller has iscsi_session::frwd_lock
>   -> iscsi_prep_mgmt_task()
>      -> session->tt->init_task() (iscsi_iser_task_init())
>         -> iser_initialize_task_headers()
>   -> session->tt->xmit_task() (
> 
> The only callchain that is close to be invoked in preemptible context:
> iscsi_xmitworker() worker
> -> iscsi_data_xmit()
>    -> iscsi_xmit_task()
>       -> conn->session->tt->xmit_task() (iscsi_iser_task_xmit()
> 
> In iscsi_iser_task_xmit() there is this check:
>    if (!task->sc)
>       return iscsi_iser_mtask_xmit(conn, task);
> 
> so it does end up in iser_initialize_task_headers() and
> iser_initialize_task_headers() relies on iscsi_task::sc == NULL.
> 
> Remove conditional locking of iser_conn::state_mutex because there is no
> call chain to do so. Remove the goto label and return early now that
> there is no clean up needed.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Max Gurtovoy <maxg@nvidia.com>
> Cc: Doug Ledford <dledford@redhat.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: linux-rdma@vger.kernel.org
> ---

Applied to for-next, thanks

Jason