linux-kernel - [RFC] auxdisplay: Fix oops on hd44780 module unloading

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Message-ID: <20210714110218.izcop7grykhfyvll@lem-wkst-02.lemonage>
Date:   Wed, 14 Jul 2021 13:02:28 +0200
From:   Lars Poeschel <poeschel@...onage.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Geert Uytterhoeven <geert.uytterhoeven@...il.com>
Subject: [RFC] auxdisplay: Fix oops on hd44780 module unloading

On Fri, Jul 09, 2021 at 07:10:14PM +0300, Andy Shevchenko wrote:
> On Fri, Jul 9, 2021 at 5:40 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> >
> > Parallel (4 bits)  panel display stopped working.
> 
> This part appears to be a configuration issue. So, we have only one
> left, i.e. oops on remove.

Could you please test, if this little change fixes the oops ?

-- >8 --

Fix this oops:
[  218.825445] kernel tried to execute NX-protected page - exploit
attempt? (uid: 0)
[  218.832965] BUG: unable to handle page fault for address: ffff8f8f06559dc0
[  218.839863] #PF: supervisor instruction fetch in kernel mode
[  218.845540] #PF: error_code(0x0011) - permissions violation
[  218.851132] PGD e601067 P4D e601067 PUD e602067 PMD 645a063 PTE
8000000006559063
[  218.858587] Oops: 0011 [#1] SMP PTI
[  218.862099] CPU: 0 PID: 7 Comm: kworker/u4:0 Tainted: G         C
     5.13.0+ #23
[  218.869870] Hardware name: Intel Corporation Merrifield/BODEGA BAY,
BIOS 542 2015.01.21:18.19.48
[  218.878681] Workqueue: kacpi_hotplug acpi_device_del_work_fn
[  218.884380] RIP: 0010:0xffff8f8f06559dc0
[  218.888328] Code: ff ff d2 2b 21 8c ff ff ff ff 08 00 00 00 00 00
00 00 78 34 fa 02 8f 8f ff ff 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 <72> 65 67 75 6c 61 74 6f 72 3a 72 65
67 75 6c 61 74 6f 72 2e 30 2d
[  218.907138] RSP: 0000:ffffad36c0043c90 EFLAGS: 00010246
[  218.912387] RAX: ffff8f8f06559dc0 RBX: ffff8f8f062cbc00 RCX: ffff8f8f01239fc8
[  218.919542] RDX: 000000002a3cccf8 RSI: 0000000000000001 RDI: ffff8f8f06559480
[  218.926701] RBP: ffffffffc037e279 R08: 00000000d5832520 R09: 0000000000000001
[  218.933856] R10: 0000000000000000 R11: 0000000000000001 R12: ffff8f8f062cbc00
[  218.941010] R13: ffffffffc038e028 R14: ffffffff8c5e0b60 R15: 00000000fffffffd
[  218.948166] FS:  0000000000000000(0000) GS:ffff8f8f3e200000(0000)
knlGS:0000000000000000
[  218.956286] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  218.962053] CR2: ffff8f8f06559dc0 CR3: 0000000002ef4000 CR4: 00000000001006f0
[  218.969208] Call Trace:
[  218.971678]  ? hd44780_common_clear_display+0x17/0x30 [hd44780_common]
[  218.978252]  ? charlcd_write_char+0x21a/0x810 [charlcd]
[  218.983519]  ? charlcd_puts+0x30/0x60 [charlcd]
[  218.988083]  ? charlcd_unregister+0x24/0x70 [charlcd]
[  218.993167]  ? hd44780_remove+0x1e/0x30 [hd44780]
[  218.997901]  ? platform_remove+0x1f/0x40

Reported-By: Andy Shevchenko <andy.shevchenko@...il.com>
Signed-off-by: Lars Poeschel <poeschel@...onage.de>
---
 drivers/auxdisplay/hd44780.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/auxdisplay/hd44780.c b/drivers/auxdisplay/hd44780.c
index 2e5e7c993933..8b2a0eb3f32a 100644
--- a/drivers/auxdisplay/hd44780.c
+++ b/drivers/auxdisplay/hd44780.c
@@ -323,8 +323,8 @@ static int hd44780_remove(struct platform_device *pdev)
 {
 	struct charlcd *lcd = platform_get_drvdata(pdev);
 
-	kfree(lcd->drvdata);
 	charlcd_unregister(lcd);
+	kfree(lcd->drvdata);
 
 	kfree(lcd);
 	return 0;
-- 
2.30.2