linux-kernel - [PATCH] bus: mhi: core: Disable pre-emption for data events tasklet processing

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Date:   Fri, 18 Jun 2021 15:23:05 -0700
From:   Bhaumik Bhatt <bbhatt@...eaurora.org>
To:     manivannan.sadhasivam@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, hemantk@...eaurora.org,
        jhugo@...eaurora.org, linux-kernel@...r.kernel.org,
        loic.poulain@...aro.org, Bhaumik Bhatt <bbhatt@...eaurora.org>
Subject: [PATCH] bus: mhi: core: Disable pre-emption for data events tasklet processing

With spin_lock_bh(), it is possible that a tasklet processing data
events gets scheduled out if another higher priority tasklet is
ready to run. While the tasklet is sleeping, it can hold the event
ring spinlock and block another tasklet, for example, one processing
an M0 state change event, from acquiring it. This can starve the
core which blocks in an attempt to acquire the spinlock until it
gets released. Fix this issue by disabling pre-emption on the core
processing data events and allow it to run to completion such that
other tasklets do not block for long periods.

Fixes: 1d3173a3bae7 ("bus: mhi: core: Add support for processing events from client device")
Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
---
 drivers/bus/mhi/core/main.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
index 3775c77..02c8c09 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -1036,11 +1036,12 @@ void mhi_ev_task(unsigned long data)
 {
 	struct mhi_event *mhi_event = (struct mhi_event *)data;
 	struct mhi_controller *mhi_cntrl = mhi_event->mhi_cntrl;
+	unsigned long flags;
 
 	/* process all pending events */
-	spin_lock_bh(&mhi_event->lock);
+	spin_lock_irqsave(&mhi_event->lock, flags);
 	mhi_event->process_event(mhi_cntrl, mhi_event, U32_MAX);
-	spin_unlock_bh(&mhi_event->lock);
+	spin_unlock_irqrestore(&mhi_event->lock, flags);
 }
 
 void mhi_ctrl_ev_task(unsigned long data)
-- 
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