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From:   Zhang Yuchen <zhangyuchen.lcr@bytedance.com>
To:     minyard@acm.org
Cc:     openipmi-developer@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, qi.zheng@linux.dev,
        Zhang Yuchen <zhangyuchen.lcr@bytedance.com>
Subject: [PATCH 2/3] ipmi: fix long wait in unload when IPMI disconnect
Date:   Fri,  7 Oct 2022 17:26:16 +0800
Message-Id: <20221007092617.87597-3-zhangyuchen.lcr@bytedance.com>
In-Reply-To: <20221007092617.87597-1-zhangyuchen.lcr@bytedance.com>
References: <20221007092617.87597-1-zhangyuchen.lcr@bytedance.com>
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When fixing the problem mentioned in PATCH1, we also found
the following problem:

If the IPMI is disconnected and in the sending process, the
uninstallation driver will be stuck for a long time.

The main problem is that uninstalling the driver waits for curr_msg to
be sent or HOSED. After stopping tasklet, the only place to trigger the
timeout mechanism is the circular poll in shutdown_smi.

The poll function delays 10us and calls smi_event_handler(smi_info,10).
Smi_event_handler deducts 10us from kcs->ibf_timeout.

But the poll func is followed by schedule_timeout_uninterruptible(1).
The time consumed here is not counted in kcs->ibf_timeout.

So when 10us is deducted from kcs->ibf_timeout, at least 1 jiffies has
actually passed. The waiting time has increased by more than a
hundredfold.

Now instead of calling poll(). call smi_event_handler() directly and
calculate the elapsed time.

For verification, you can directly use ebpf to check the kcs->
ibf_timeout for each call to kcs_event() when IPMI is disconnected.
Decrement at normal rate before unloading. The decrement rate becomes
very slow after unloading.

  $ bpftrace -e 'kprobe:kcs_event {printf("kcs->ibftimeout : %d\n",
      *(arg0+584));}'

Signed-off-by: Zhang Yuchen <zhangyuchen.lcr@bytedance.com>
---
 drivers/char/ipmi/ipmi_si_intf.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
index 6e357ad76f2e..abddd7e43a9a 100644
--- a/drivers/char/ipmi/ipmi_si_intf.c
+++ b/drivers/char/ipmi/ipmi_si_intf.c
@@ -2153,6 +2153,20 @@ static int __init init_ipmi_si(void)
 }
 module_init(init_ipmi_si);
 
+static void wait_msg_processed(struct smi_info *smi_info)
+{
+	unsigned long jiffies_now;
+	long time_diff;
+
+	while (smi_info->curr_msg || (smi_info->si_state != SI_NORMAL)) {
+		jiffies_now = jiffies;
+		time_diff = (((long)jiffies_now - (long)smi_info->last_timeout_jiffies)
+		     * SI_USEC_PER_JIFFY);
+		smi_event_handler(smi_info, time_diff);
+		schedule_timeout_uninterruptible(1);
+	}
+}
+
 static void shutdown_smi(void *send_info)
 {
 	struct smi_info *smi_info = send_info;
@@ -2187,16 +2201,13 @@ static void shutdown_smi(void *send_info)
 	 * in the BMC.  Note that timers and CPU interrupts are off,
 	 * so no need for locks.
 	 */
-	while (smi_info->curr_msg || (smi_info->si_state != SI_NORMAL)) {
-		poll(smi_info);
-		schedule_timeout_uninterruptible(1);
-	}
+	wait_msg_processed(smi_info);
+
 	if (smi_info->handlers)
 		disable_si_irq(smi_info);
-	while (smi_info->curr_msg || (smi_info->si_state != SI_NORMAL)) {
-		poll(smi_info);
-		schedule_timeout_uninterruptible(1);
-	}
+
+	wait_msg_processed(smi_info);
+
 	if (smi_info->handlers)
 		smi_info->handlers->cleanup(smi_info->si_sm);
 
-- 
2.30.2