linux-kernel - [PATCH] soc: qcom: qmi: Signal the txn completion after releasing the mutex

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Date:   Mon, 31 Jul 2023 18:37:55 +0530
From:   Praveenkumar I <quic_ipkumar@...cinc.com>
To:     <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <clew@...eaurora.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <quic_varada@...cinc.com>, <quic_srichara@...cinc.com>
Subject: [PATCH] soc: qcom: qmi: Signal the txn completion after releasing the mutex

txn is in #1 stack

Worker #1                                       Worker #2
********					*********

qmi_txn_wait(txn)                               qmi_handle_message
   |                                                  |
   |                                                  |
 wait_for_complete(txn->complete)                    ....
   |                                             mutex_lock(txn->lock)
   |                                                  |
 mutex_lock(txn->lock)                                |
   .....                                         complete(txn->lock)
   |                                             mutex_unlock(txn->lock)
   |
 mutex_unlock(txn->lock)

In this case above, while #2 is doing the mutex_unlock(txn->lock),
in between releasing lock and doing other lock related wakeup, #2 gets
scheduled out. As a result #1, acquires the lock, unlocks, also
frees the txn also (where the lock resides)

Now #2, gets scheduled again and tries to do the rest of the lock
related wakeup, but lock itself is invalid because txn itself is gone.

Fixing this, by doing the mutex_unlock(txn->lock) first and then
complete(txn->lock) in #2

Fixes: 3830d0771ef6 ("soc: qcom: Introduce QMI helpers")
Cc: stable@...r.kernel.org
Signed-off-by: Sricharan Ramabadhran <quic_srichara@...cinc.com>
Signed-off-by: Praveenkumar I <quic_ipkumar@...cinc.com>
---
 drivers/soc/qcom/qmi_interface.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soc/qcom/qmi_interface.c b/drivers/soc/qcom/qmi_interface.c
index 78d7361fdcf2..92e29db97359 100644
--- a/drivers/soc/qcom/qmi_interface.c
+++ b/drivers/soc/qcom/qmi_interface.c
@@ -505,12 +505,13 @@ static void qmi_handle_message(struct qmi_handle *qmi,
 				pr_err("failed to decode incoming message\n");
 
 			txn->result = ret;
-			complete(&txn->completion);
 		} else  {
 			qmi_invoke_handler(qmi, sq, txn, buf, len);
 		}
 
 		mutex_unlock(&txn->lock);
+		if (txn->dest && txn->ei)
+			complete(&txn->completion);
 	} else {
 		/* Create a txn based on the txn_id of the incoming message */
 		memset(&tmp_txn, 0, sizeof(tmp_txn));
-- 
2.34.1