linux-kernel - [PATCH] driver core: bus: Handle early calls to bus_to

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Message-Id: <0a92979f6e790737544638e8a4c19b0564e660a2.1676983596.git.geert+renesas@glider.be>
Date:   Tue, 21 Feb 2023 13:53:51 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Lee Jones <lee@...nel.org>,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] driver core: bus: Handle early calls to bus_to_subsys()

When calling soc_device_match() from early_initcall(), bus_kset is still
NULL, causing a crash:

    Unable to handle kernel NULL pointer dereference at virtual address 0000000000000028
    ...
    Call trace:
     __lock_acquire+0x530/0x20f0
     lock_acquire.part.0+0xc8/0x210
     lock_acquire+0x64/0x80
     _raw_spin_lock+0x4c/0x60
     bus_to_subsys+0x24/0xac
     bus_for_each_dev+0x30/0xcc
     soc_device_match+0x4c/0xe0
     r8a7795_sysc_init+0x18/0x60
     rcar_sysc_pd_init+0xb0/0x33c
     do_one_initcall+0x128/0x2bc

Before, bus_for_each_dev() handled this gracefully by checking that
the back-pointer to the private structure was valid.

Fix this by adding a NULL check for bus_kset to bus_to_subsys().

Fixes: 83b9148df2c95e23 ("driver core: bus: bus iterator cleanups")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 drivers/base/bus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index cfe8615d5106f030..dd4b82d7510f68fb 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -62,7 +62,7 @@ static struct subsys_private *bus_to_subsys(const struct bus_type *bus)
 	struct subsys_private *sp = NULL;
 	struct kobject *kobj;
 
-	if (!bus)
+	if (!bus || !bus_kset)
 		return NULL;
 
 	spin_lock(&bus_kset->list_lock);
-- 
2.34.1