[PATCH AUTOSEL 3.18 45/61] fbdev: fbcon: Fix unregister crash when more than one framebuffer

Sasha Levin
2019-01-28T16:27:50Z

From: Noralf Trønnes <noralf@tronnes.org>

[ Upstream commit 2122b40580dd9d0620398739c773d07a7b7939d0 ]

When unregistering fbdev using unregister_framebuffer(), any bound
console will unbind automatically. This is working fine if this is the
only framebuffer, resulting in a switch to the dummy console. However if
there is a fb0 and I unregister fb1 having a bound console, I eventually
get a crash. The fastest way for me to trigger the crash is to do a
reboot, resulting in this splat:

[ 76.478825] WARNING: CPU: 0 PID: 527 at linux/kernel/workqueue.c:1442 __queue_work+0x2d4/0x41c
[ 76.478849] Modules linked in: raspberrypi_hwmon gpio_backlight backlight bcm2835_rng rng_core [last unloaded: tinydrm]
[ 76.478916] CPU: 0 PID: 527 Comm: systemd-udevd Not tainted 4.20.0-rc4+ #4
[ 76.478933] Hardware name: BCM2835
[ 76.478949] Backtrace:
[ 76.478995] [<c010d388>] (dump_backtrace) from [<c010d670>] (show_stack+0x20/0x24)
[ 76.479022] r6:00000000 r5:c0bc73be r4:00000000 r3:6fb5bf81
[ 76.479060] [<c010d650>] (show_stack) from [<c08e82f4>] (dump_stack+0x20/0x28)
[ 76.479102] [<c08e82d4>] (dump_stack) from [<c0120070>] (__warn+0xec/0x12c)
[ 76.479134] [<c011ff84>] (__warn) from [<c01201e4>] (warn_slowpath_null+0x4c/0x58)
[ 76.479165] r9:c0eb6944 r8:00000001 r7:c0e927f8 r6:c0bc73be r5:000005a2 r4:c0139e84
[ 76.479197] [<c0120198>] (warn_slowpath_null) from [<c0139e84>] (__queue_work+0x2d4/0x41c)
[ 76.479222] r6:d7666a00 r5:c0e918ee r4:dbc4e700
[ 76.479251] [<c0139bb0>] (__queue_work) from [<c013a02c>] (queue_work_on+0x60/0x88)
[ 76.479281] r10:c0496bf8 r9:00000100 r8:c0e92ae0 r7:00000001 r6:d9403700 r5:d7666a00
[ 76.479298] r4:20000113
[ 76.479348] [<c0139fcc>] (queue_work_on) from [<c0496c28>] (cursor_timer_handler+0x30/0x54)
[ 76.479374] r7:d8a8fabc r6:c0e08088 r5:d8afdc5c r4:d8a8fabc
[ 76.479413] [<c0496bf8>] (cursor_timer_handler) from [<c0178744>] (call_timer_fn+0x100/0x230)
[ 76.479435] r4:c0e9192f r3:d758a340
[ 76.479465] [<c0178644>] (call_timer_fn) from [<c0178980>] (expire_timers+0x10c/0x12c)
[ 76.479495] r10:40000000 r9:c0e9192f r8:c0e92ae0 r7:d8afdccc r6:c0e19280 r5:c0496bf8
[ 76.479513] r4:d8a8fabc
[ 76.479541] [<c0178874>] (expire_timers) from [<c0179630>] (run_timer_softirq+0xa8/0x184)
[ 76.479570] r9:00000001 r8:c0e19280 r7:00000000 r6:c0e08088 r5:c0e1a3e0 r4:c0e19280
[ 76.479603] [<c0179588>] (run_timer_softirq) from [<c0102404>] (__do_softirq+0x1ac/0x3fc)
[ 76.479632] r10:c0e91680 r9:d8afc020 r8:0000000a r7:00000100 r6:00000001 r5:00000002
[ 76.479650] r4:c0eb65ec
[ 76.479686] [<c0102258>] (__do_softirq) from [<c0124d10>] (irq_exit+0xe8/0x168)
[ 76.479716] r10:d8d1a9b0 r9:d8afc000 r8:00000001 r7:d949c000 r6:00000000 r5:c0e8b3f0
[ 76.479734] r4:00000000
[ 76.479764] [<c0124c28>] (irq_exit) from [<c016b72c>] (__handle_domain_irq+0x94/0xb0)
[ 76.479793] [<c016b698>] (__handle_domain_irq) from [<c01021dc>] (bcm2835_handle_irq+0x3c/0x48)
[ 76.479823] r8:d8afdebc r7:d8afddfc r6:ffffffff r5:c0e089f8 r4:d8afddc8 r3:d8afddc8
[ 76.479851] [<c01021a0>] (bcm2835_handle_irq) from [<c01019f0>] (__irq_svc+0x70/0x98)

The problem is in the console rebinding in fbcon_fb_unbind(). It uses the
virtual console index as the new framebuffer index to bind the console(s)
to. The correct way is to use the con2fb_map lookup table to find the
framebuffer index.

Fixes: cfafca8067c6 ("fbdev: fbcon: console unregistration from unregister_framebuffer")
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/video/console/fbcon.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index eb976ee3a02f..614d3209d465 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -3018,7 +3018,7 @@ static int fbcon_fb_unbind(int idx)
for (i = first_fb_vc; i <= last_fb_vc; i++) {
if (con2fb_map[i] != idx &&
con2fb_map[i] != -1) {
- new_idx = i;
+ new_idx = con2fb_map[i];
break;
}
}
--
2.19.1