Subject: Re: [PATCH 6/9] ipmi: Convert from tasklet to BH workqueue

From: Corey Minyard <[email-masked]>
Date: Wed, 27 Mar 2024 12:58:23 -0500

On Wed, Mar 27, 2024 at 04:03:11PM +0000, Allen Pais wrote:
> The only generic interface to execute asynchronously in the BH context is
> tasklet; however, it's marked deprecated and has some design flaws. To
> replace tasklets, BH workqueue support was recently added. A BH workqueue
> behaves similarly to regular workqueues except that the queued work items
> are executed in the BH context.
> 
> This patch converts drivers/infiniband/* from tasklet to BH workqueue.

I think you mean drivers/char/ipmi/* here.

I believe that work queues items are execute single-threaded for a work
queue, so this should be good.  I need to test this, though.  It may be
that an IPMI device can have its own work queue; it may not be important
to run it in bh context.

-corey

> 
> Based on the work done by Tejun Heo <[email-masked]>
> Branch: https://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-6.10
> 
> Signed-off-by: Allen Pais <[email-masked]>
> ---
>  drivers/char/ipmi/ipmi_msghandler.c | 30 ++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index b0eedc4595b3..fce2a2dbdc82 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -36,12 +36,13 @@
>  #include <linux/nospec.h>
>  #include <linux/vmalloc.h>
>  #include <linux/delay.h>
> +#include <linux/workqueue.h>
>  
>  #define IPMI_DRIVER_VERSION "39.2"
>  
>  static struct ipmi_recv_msg *ipmi_alloc_recv_msg(void);
>  static int ipmi_init_msghandler(void);
> -static void smi_recv_tasklet(struct tasklet_struct *t);
> +static void smi_recv_work(struct work_struct *t);
>  static void handle_new_recv_msgs(struct ipmi_smi *intf);
>  static void need_waiter(struct ipmi_smi *intf);
>  static int handle_one_recv_msg(struct ipmi_smi *intf,
> @@ -498,13 +499,13 @@ struct ipmi_smi {
>  	/*
>  	 * Messages queued for delivery.  If delivery fails (out of memory
>  	 * for instance), They will stay in here to be processed later in a
> -	 * periodic timer interrupt.  The tasklet is for handling received
> +	 * periodic timer interrupt.  The work is for handling received
>  	 * messages directly from the handler.
>  	 */
>  	spinlock_t       waiting_rcv_msgs_lock;
>  	struct list_head waiting_rcv_msgs;
>  	atomic_t	 watchdog_pretimeouts_to_deliver;
> -	struct tasklet_struct recv_tasklet;
> +	struct work_struct recv_work;
>  
>  	spinlock_t             xmit_msgs_lock;
>  	struct list_head       xmit_msgs;
> @@ -704,7 +705,7 @@ static void clean_up_interface_data(struct ipmi_smi *intf)
>  	struct cmd_rcvr  *rcvr, *rcvr2;
>  	struct list_head list;
>  
> -	tasklet_kill(&intf->recv_tasklet);
> +	cancel_work_sync(&intf->recv_work);
>  
>  	free_smi_msg_list(&intf->waiting_rcv_msgs);
>  	free_recv_msg_list(&intf->waiting_events);
> @@ -1319,7 +1320,7 @@ static void free_user(struct kref *ref)
>  {
>  	struct ipmi_user *user = container_of(ref, struct ipmi_user, refcount);
>  
> -	/* SRCU cleanup must happen in task context. */
> +	/* SRCU cleanup must happen in work context. */
>  	queue_work(remove_work_wq, &user->remove_work);
>  }
>  
> @@ -3605,8 +3606,7 @@ int ipmi_add_smi(struct module         *owner,
>  	intf->curr_seq = 0;
>  	spin_lock_init(&intf->waiting_rcv_msgs_lock);
>  	INIT_LIST_HEAD(&intf->waiting_rcv_msgs);
> -	tasklet_setup(&intf->recv_tasklet,
> -		     smi_recv_tasklet);
> +	INIT_WORK(&intf->recv_work, smi_recv_work);
>  	atomic_set(&intf->watchdog_pretimeouts_to_deliver, 0);
>  	spin_lock_init(&intf->xmit_msgs_lock);
>  	INIT_LIST_HEAD(&intf->xmit_msgs);
> @@ -4779,7 +4779,7 @@ static void handle_new_recv_msgs(struct ipmi_smi *intf)
>  			 * To preserve message order, quit if we
>  			 * can't handle a message.  Add the message
>  			 * back at the head, this is safe because this
> -			 * tasklet is the only thing that pulls the
> +			 * work is the only thing that pulls the
>  			 * messages.
>  			 */
>  			list_add(&smi_msg->link, &intf->waiting_rcv_msgs);
> @@ -4812,10 +4812,10 @@ static void handle_new_recv_msgs(struct ipmi_smi *intf)
>  	}
>  }
>  
> -static void smi_recv_tasklet(struct tasklet_struct *t)
> +static void smi_recv_work(struct work_struct *t)
>  {
>  	unsigned long flags = 0; /* keep us warning-free. */
> -	struct ipmi_smi *intf = from_tasklet(intf, t, recv_tasklet);
> +	struct ipmi_smi *intf = from_work(intf, t, recv_work);
>  	int run_to_completion = intf->run_to_completion;
>  	struct ipmi_smi_msg *newmsg = NULL;
>  
> @@ -4866,7 +4866,7 @@ void ipmi_smi_msg_received(struct ipmi_smi *intf,
>  
>  	/*
>  	 * To preserve message order, we keep a queue and deliver from
> -	 * a tasklet.
> +	 * a work.
>  	 */
>  	if (!run_to_completion)
>  		spin_lock_irqsave(&intf->waiting_rcv_msgs_lock, flags);
> @@ -4887,9 +4887,9 @@ void ipmi_smi_msg_received(struct ipmi_smi *intf,
>  		spin_unlock_irqrestore(&intf->xmit_msgs_lock, flags);
>  
>  	if (run_to_completion)
> -		smi_recv_tasklet(&intf->recv_tasklet);
> +		smi_recv_work(&intf->recv_work);
>  	else
> -		tasklet_schedule(&intf->recv_tasklet);
> +		queue_work(system_bh_wq, &intf->recv_work);
>  }
>  EXPORT_SYMBOL(ipmi_smi_msg_received);
>  
> @@ -4899,7 +4899,7 @@ void ipmi_smi_watchdog_pretimeout(struct ipmi_smi *intf)
>  		return;
>  
>  	atomic_set(&intf->watchdog_pretimeouts_to_deliver, 1);
> -	tasklet_schedule(&intf->recv_tasklet);
> +	queue_work(system_bh_wq, &intf->recv_work);
>  }
>  EXPORT_SYMBOL(ipmi_smi_watchdog_pretimeout);
>  
> @@ -5068,7 +5068,7 @@ static bool ipmi_timeout_handler(struct ipmi_smi *intf,
>  				       flags);
>  	}
>  
> -	tasklet_schedule(&intf->recv_tasklet);
> +	queue_work(system_bh_wq, &intf->recv_work);
>  
>  	return need_timer;
>  }
> -- 
> 2.17.1
> 
>