linux-kernel - [PATCH] PM / devfreq: Return -ENODEV from try_then_request

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Message-Id: <20190423081158.29859-1-tomeu.vizoso@collabora.com>
Date:   Tue, 23 Apr 2019 10:11:56 +0200
From:   Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:     linux-kernel@...r.kernel.org
Cc:     Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>, linux-pm@...r.kernel.org
Subject: [PATCH] PM / devfreq: Return -ENODEV from try_then_request_governor

Callers don't expect it to return NULL, but an error code.

Fixes Oops such as the one below, when one tries to set a governor that
isn't available:

Unable to handle kernel NULL pointer dereference at virtual address 00000018

[<c0dcf718>] (governor_store) from [<c0539558>] (kernfs_fop_write+0x100/0x1e0)
[<c0539558>] (kernfs_fop_write) from [<c04b09b4>] (__vfs_write+0x2c/0x17c)
[<c04b09b4>] (__vfs_write) from [<c04b33fc>] (vfs_write+0xa4/0x184)
[<c04b33fc>] (vfs_write) from [<c04b361c>] (ksys_write+0x4c/0xac)
[<c04b361c>] (ksys_write) from [<c0301000>] (ret_fast_syscall+0x0/0x28)

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
Fixes: 23c7b54ca1cd ("PM / devfreq: Fix devfreq_add_device() when drivers are built as modules.")
Reported-by: Alyssa Rosenzweig <alyssa@...enzweig.io>
Cc: Enric Balletbo i Serra <enric.balletbo@...labora.com>
---
 drivers/devfreq/devfreq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 0ae3de76833b..5539e9be718d 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -254,7 +254,7 @@ static struct devfreq_governor *try_then_request_governor(const char *name)
 		/* Restore previous state before return */
 		mutex_lock(&devfreq_list_lock);
 		if (err)
-			return NULL;
+			return ERR_PTR(-ENODEV);
 
 		governor = find_devfreq_governor(name);
 	}
-- 
2.20.1