Re: [PATCH 3/6] ipmi: use a tasklet for handling received messages

From: Corey Minyard
Date: Fri Feb 03 2012 - 15:01:44 EST

On 02/03/2012 01:44 PM, Andrew Morton wrote:
On Fri, 03 Feb 2012 09:47:56 -0600
Corey Minyard<cminyard@xxxxxxxxxx> wrote:

The IPMI driver would release a lock, deliver a message, then relock.
This is obviously ugly, and this patch converts the message handler
interface to use a tasklet to schedule work. This lets the receive
handler be called from an interrupt handler with interrupts enabled.


+ * If there are messages in the queue or pretimeouts, handle them.
+ */
+static void handle_new_recv_msgs(ipmi_smi_t intf)
+ struct ipmi_smi_msg *smi_msg;
+ unsigned long flags = 0;
+ int rv;
+ int run_to_completion = intf->run_to_completion;
+ /* See if any waiting messages need to be processed. */
+ if (!run_to_completion)
+ spin_lock_irqsave(&intf->waiting_msgs_lock, flags);
+ while (!list_empty(&intf->waiting_msgs)) {
+ smi_msg = list_entry(intf->,
+ struct ipmi_smi_msg, link);
+ list_del(&smi_msg->link);
+ if (!run_to_completion)
+ spin_unlock_irqrestore(&intf->waiting_msgs_lock, flags);
Yikes, what's going on here? How is the list protected if the spinlock
isn't taken?

I went to the comment over ipmi_smi.run_to_completion but it doesn't
explain how it governs the locking strategy at all. If there's some
other way in which the reader is supposed to grok IPMI locking, please
clue me in ;)

The "run_to_completion" mode is designed to run at panic time so that the watchdog timer can be extended and panic information can be stored in the IPMI event log. In that case locks are irrelevant and can cause hangs, so they are skipped.

This is documented a little better in ipmi_si_intf.c, but you are right, it's not terribly complete.

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