[PATCH v3] ipmi: Add limits to event and receive message requests

[Corey Minyard <corey@minyard.net>]

The driver would just fetch events and receive messages until the
BMC said it was done.  To avoid issues with BMCs that never say they are
done, add a limit of 10 fetches at a time.

In addition, an si interface has an attn state it can return from the
hardware which is supposed to cause a flag fetch to see if the driver
needs to fetch events or message or a few other things.  If the attn
bit gets stuck, it's a similar problem.  So allow messages in between
flag fetches so the driver itself doesn't get stuck.

This is a more general fix than the previous fix for the specific bad
BMC, but should fix the more general issue of a BMC that won't stop
saying it has data.

This has been there from the beginning of the driver.  It's not a bug
per-se, but it is accounting for bugs in BMCs.

Reported-by: Matt Fleming <mfleming@cloudflare.com>
Closes: https://lore.kernel.org/lkml/20260415115930.3428942-1-matt@readmodwrite.com/
Fixes: <1da177e4c3f4> ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Corey Minyard <corey@minyard.net>
---
I have added this problem as a capability in the openipmi library
simulator so I can reproduce the issue and make sure everything works
properly.

 drivers/char/ipmi/ipmi_si_intf.c | 54 +++++++++++++++++++++++++-------
 drivers/char/ipmi/ipmi_ssif.c    | 23 ++++++++++++--
 2 files changed, 64 insertions(+), 13 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
index 08c208cc64c5..7c3c463e08da 100644
--- a/drivers/char/ipmi/ipmi_si_intf.c
+++ b/drivers/char/ipmi/ipmi_si_intf.c
@@ -168,6 +168,10 @@ struct smi_info {
 			     OEM2_DATA_AVAIL)
 	unsigned char       msg_flags;
 
+	/* When requesting events and messages, don't do it forever. */
+	unsigned int        num_requests_in_a_row;
+	bool		    last_was_flag_fetch;
+
 	/* Does the BMC have an event buffer? */
 	bool		    has_event_buffer;
 
@@ -410,7 +414,10 @@ static void start_getting_msg_queue(struct smi_info *smi_info)
 
 	start_new_msg(smi_info, smi_info->curr_msg->data,
 		      smi_info->curr_msg->data_size);
-	smi_info->si_state = SI_GETTING_MESSAGES;
+	if (smi_info->si_state != SI_GETTING_MESSAGES) {
+		smi_info->num_requests_in_a_row = 0;
+		smi_info->si_state = SI_GETTING_MESSAGES;
+	}
 }
 
 static void start_getting_events(struct smi_info *smi_info)
@@ -421,7 +428,10 @@ static void start_getting_events(struct smi_info *smi_info)
 
 	start_new_msg(smi_info, smi_info->curr_msg->data,
 		      smi_info->curr_msg->data_size);
-	smi_info->si_state = SI_GETTING_EVENTS;
+	if (smi_info->si_state != SI_GETTING_EVENTS) {
+		smi_info->num_requests_in_a_row = 0;
+		smi_info->si_state = SI_GETTING_EVENTS;
+	}
 }
 
 /*
@@ -595,6 +605,7 @@ static void handle_transaction_done(struct smi_info *smi_info)
 			smi_info->si_state = SI_NORMAL;
 		} else {
 			smi_info->msg_flags = msg[3];
+			smi_info->last_was_flag_fetch = true;
 			handle_flags(smi_info);
 		}
 		break;
@@ -646,6 +657,11 @@ static void handle_transaction_done(struct smi_info *smi_info)
 		} else {
 			smi_inc_stat(smi_info, events);
 
+			smi_info->num_requests_in_a_row++;
+			if (smi_info->num_requests_in_a_row > 10)
+				/* Stop if we do this too many times. */
+				smi_info->msg_flags &= ~EVENT_MSG_BUFFER_FULL;
+
 			/*
 			 * Do this before we deliver the message
 			 * because delivering the message releases the
@@ -684,6 +700,11 @@ static void handle_transaction_done(struct smi_info *smi_info)
 		} else {
 			smi_inc_stat(smi_info, incoming_messages);
 
+			smi_info->num_requests_in_a_row++;
+			if (smi_info->num_requests_in_a_row > 10)
+				/* Stop if we do this too many times. */
+				smi_info->msg_flags &= ~RECEIVE_MSG_AVAIL;
+
 			/*
 			 * Do this before we deliver the message
 			 * because delivering the message releases the
@@ -825,6 +846,26 @@ static enum si_sm_result smi_event_handler(struct smi_info *smi_info,
 		goto out;
 	}
 
+	/*
+	 * If we are currently idle, or if the last thing that was
+	 * done was a flag fetch and there is a message pending, try
+	 * to start the next message.
+	 *
+	 * We do the waiting message check to avoid a stuck flag
+	 * completely wedging the driver.  Let a message through
+	 * in between flag operations if that happens.
+	 */
+	if (si_sm_result == SI_SM_IDLE ||
+	    (si_sm_result == SI_SM_ATTN && smi_info->waiting_msg &&
+	     smi_info->last_was_flag_fetch)) {
+		smi_info->last_was_flag_fetch = false;
+		smi_inc_stat(smi_info, idles);
+
+		si_sm_result = start_next_msg(smi_info);
+		if (si_sm_result != SI_SM_IDLE)
+			goto restart;
+	}
+
 	/*
 	 * We prefer handling attn over new messages.  But don't do
 	 * this if there is not yet an upper layer to handle anything.
@@ -852,15 +893,6 @@ static enum si_sm_result smi_event_handler(struct smi_info *smi_info,
 		}
 	}
 
-	/* If we are currently idle, try to start the next message. */
-	if (si_sm_result == SI_SM_IDLE) {
-		smi_inc_stat(smi_info, idles);
-
-		si_sm_result = start_next_msg(smi_info);
-		if (si_sm_result != SI_SM_IDLE)
-			goto restart;
-	}
-
 	if ((si_sm_result == SI_SM_IDLE)
 	    && (atomic_read(&smi_info->req_events))) {
 		/*
diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
index b49500a1bd36..f3798f4e6a63 100644
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -225,6 +225,9 @@ struct ssif_info {
 	bool		    has_event_buffer;
 	bool		    supports_alert;
 
+	/* When requesting events and messages, don't do it forever. */
+	unsigned int        num_requests_in_a_row;
+
 	/*
 	 * Used to tell what we should do with alerts.  If we are
 	 * waiting on a response, read the data immediately.
@@ -413,7 +416,10 @@ static void start_event_fetch(struct ssif_info *ssif_info, unsigned long *flags)
 	}
 
 	ssif_info->curr_msg = msg;
-	ssif_info->ssif_state = SSIF_GETTING_EVENTS;
+	if (ssif_info->ssif_state != SSIF_GETTING_EVENTS) {
+		ssif_info->num_requests_in_a_row = 0;
+		ssif_info->ssif_state = SSIF_GETTING_EVENTS;
+	}
 	ipmi_ssif_unlock_cond(ssif_info, flags);
 
 	msg->data[0] = (IPMI_NETFN_APP_REQUEST << 2);
@@ -436,7 +442,10 @@ static void start_recv_msg_fetch(struct ssif_info *ssif_info,
 	}
 
 	ssif_info->curr_msg = msg;
-	ssif_info->ssif_state = SSIF_GETTING_MESSAGES;
+	if (ssif_info->ssif_state != SSIF_GETTING_MESSAGES) {
+		ssif_info->num_requests_in_a_row = 0;
+		ssif_info->ssif_state = SSIF_GETTING_MESSAGES;
+	}
 	ipmi_ssif_unlock_cond(ssif_info, flags);
 
 	msg->data[0] = (IPMI_NETFN_APP_REQUEST << 2);
@@ -843,6 +852,11 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 			ssif_info->msg_flags &= ~EVENT_MSG_BUFFER_FULL;
 			handle_flags(ssif_info, flags);
 		} else {
+			ssif_info->num_requests_in_a_row++;
+			if (ssif_info->num_requests_in_a_row > 10)
+				/* Stop if we do this too many times. */
+				ssif_info->msg_flags &= ~EVENT_MSG_BUFFER_FULL;
+
 			handle_flags(ssif_info, flags);
 			ssif_inc_stat(ssif_info, events);
 			deliver_recv_msg(ssif_info, msg);
@@ -876,6 +890,11 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 			ssif_info->msg_flags &= ~RECEIVE_MSG_AVAIL;
 			handle_flags(ssif_info, flags);
 		} else {
+			ssif_info->num_requests_in_a_row++;
+			if (ssif_info->num_requests_in_a_row > 10)
+				/* Stop if we do this too many times. */
+				ssif_info->msg_flags &= ~RECEIVE_MSG_AVAIL;
+
 			ssif_inc_stat(ssif_info, incoming_messages);
 			handle_flags(ssif_info, flags);
 			deliver_recv_msg(ssif_info, msg);
-- 
2.43.0