linux-kernel - [PATCH] spmi: Add a check for remove callback when removing a SPMI driver

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Date:   Wed, 21 Dec 2022 11:07:12 +0530
From:   Jishnu Prakash <quic_jprakash@...cinc.com>
To:     <gregkh@...uxfoundation.org>, <sboyd@...nel.org>,
        <agross@...nel.org>, <devicetree@...r.kernel.org>,
        <robh+dt@...nel.org>, <linus.walleij@...aro.org>,
        <quic_kamalw@...cinc.com>, <quic_subbaram@...cinc.com>,
        <quic_collinsd@...cinc.com>, <linux-kernel@...r.kernel.org>
CC:     <linux-arm-msm@...r.kernel.org>,
        <linux-arm-msm-owner@...r.kernel.org>,
        Jishnu Prakash <quic_jprakash@...cinc.com>
Subject: [PATCH] spmi: Add a check for remove callback when removing a SPMI driver

When removing a SPMI driver, there can be a crash due to NULL pointer
dereference if it does not have a remove callback defined. This is
one such call trace observed when removing the QCOM SPMI PMIC driver:

 dump_backtrace.cfi_jt+0x0/0x8
 dump_stack_lvl+0xd8/0x16c
 panic+0x188/0x498
 __cfi_slowpath+0x0/0x214
 __cfi_slowpath+0x1dc/0x214
 spmi_drv_remove+0x16c/0x1e0
 device_release_driver_internal+0x468/0x79c
 driver_detach+0x11c/0x1a0
 bus_remove_driver+0xc4/0x124
 driver_unregister+0x58/0x84
 cleanup_module+0x1c/0xc24 [qcom_spmi_pmic]
 __do_sys_delete_module+0x3ec/0x53c
 __arm64_sys_delete_module+0x18/0x28
 el0_svc_common+0xdc/0x294
 el0_svc+0x38/0x9c
 el0_sync_handler+0x8c/0xf0
 el0_sync+0x1b4/0x1c0

If a driver has all its resources allocated through devm_() APIs and
does not need any other explicit cleanup, it would not require a
remove callback to be defined. Hence, add a check for remove callback
presence before calling it when removing a SPMI driver.

Signed-off-by: Jishnu Prakash <quic_jprakash@...cinc.com>
---
 drivers/spmi/spmi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/spmi/spmi.c b/drivers/spmi/spmi.c
index a456ce5..6b34356 100644
--- a/drivers/spmi/spmi.c
+++ b/drivers/spmi/spmi.c
@@ -350,7 +350,8 @@ static void spmi_drv_remove(struct device *dev)
 	const struct spmi_driver *sdrv = to_spmi_driver(dev->driver);
 
 	pm_runtime_get_sync(dev);
-	sdrv->remove(to_spmi_device(dev));
+	if (sdrv->remove)
+		sdrv->remove(to_spmi_device(dev));
 	pm_runtime_put_noidle(dev);
 
 	pm_runtime_disable(dev);
-- 
2.7.4