[PATCH] fbdev: Fix unregistering of framebuffers without device
Thomas Zimmermann
tzimmermann at suse.de
Tue Apr 5 18:24:04 UTC 2022
Hi
Am 05.04.22 um 11:01 schrieb Daniel Vetter:
> On Mon, Apr 04, 2022 at 09:44:02PM +0200, Thomas Zimmermann wrote:
>> OF framebuffers do not have an underlying device in the Linux
>> device hierarchy. Do a regular unregister call instead of hot
>> unplugging such a non-existing device. Fixes a NULL dereference.
>> An example error message on ppc64le is shown below.
>>
>> BUG: Kernel NULL pointer dereference on read at 0x00000060
>> Faulting instruction address: 0xc00000000080dfa4
>> Oops: Kernel access of bad area, sig: 11 [#1]
>> LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
>> [...]
>> CPU: 2 PID: 139 Comm: systemd-udevd Not tainted 5.17.0-ae085d7f9365 #1
>> NIP: c00000000080dfa4 LR: c00000000080df9c CTR: c000000000797430
>> REGS: c000000004132fe0 TRAP: 0300 Not tainted (5.17.0-ae085d7f9365)
>> MSR: 8000000002009033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 28228282 XER: 20000000
>> CFAR: c00000000000c80c DAR: 0000000000000060 DSISR: 40000000 IRQMASK: 0
>> GPR00: c00000000080df9c c000000004133280 c00000000169d200 0000000000000029
>> GPR04: 00000000ffffefff c000000004132f90 c000000004132f88 0000000000000000
>> GPR08: c0000000015658f8 c0000000015cd200 c0000000014f57d0 0000000048228283
>> GPR12: 0000000000000000 c00000003fffe300 0000000020000000 0000000000000000
>> GPR16: 0000000000000000 0000000113fc4a40 0000000000000005 0000000113fcfb80
>> GPR20: 000001000f7283b0 0000000000000000 c000000000e4a588 c000000000e4a5b0
>> GPR24: 0000000000000001 00000000000a0000 c008000000db0168 c0000000021f6ec0
>> GPR28: c0000000016d65a8 c000000004b36460 0000000000000000 c0000000016d64b0
>> NIP [c00000000080dfa4] do_remove_conflicting_framebuffers+0x184/0x1d0
>> [c000000004133280] [c00000000080df9c] do_remove_conflicting_framebuffers+0x17c/0x1d0 (unreliable)
>> [c000000004133350] [c00000000080e4d0] remove_conflicting_framebuffers+0x60/0x150
>> [c0000000041333a0] [c00000000080e6f4] remove_conflicting_pci_framebuffers+0x134/0x1b0
>> [c000000004133450] [c008000000e70438] drm_aperture_remove_conflicting_pci_framebuffers+0x90/0x100 [drm]
>> [c000000004133490] [c008000000da0ce4] bochs_pci_probe+0x6c/0xa64 [bochs]
>> [...]
>> [c000000004133db0] [c00000000002aaa0] system_call_exception+0x170/0x2d0
>> [c000000004133e10] [c00000000000c3cc] system_call_common+0xec/0x250
>>
>> The bug [1] was introduced by commit 27599aacbaef ("fbdev: Hot-unplug
>> firmware fb devices on forced removal"). Most firmware framebuffers
>> have an underlying platform device, which can be hot-unplugged
>> before loading the native graphics driver. OF framebuffers do not
>> (yet) have that device. Fix the code by unregistering the framebuffer
>> as before without a hot unplug.
>>
>> Tested with 5.17 on qemu ppc64le emulation.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal")
>> Reported-by: Sudip Mukherjee <sudipm.mukherjee at gmail.com>
>> Cc: Zack Rusin <zackr at vmware.com>
>> Cc: Javier Martinez Canillas <javierm at redhat.com>
>> Cc: Hans de Goede <hdegoede at redhat.com>
>> Cc: stable at vger.kernel.org # v5.11+
>> Cc: Helge Deller <deller at gmx.de>
>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> Cc: Sam Ravnborg <sam at ravnborg.org>
>> Cc: Zheyu Ma <zheyuma97 at gmail.com>
>> Cc: Xiyu Yang <xiyuyang19 at fudan.edu.cn>
>> Cc: Zhen Lei <thunder.leizhen at huawei.com>
>> Cc: Matthew Wilcox <willy at infradead.org>
>> Cc: Alex Deucher <alexander.deucher at amd.com>
>> Cc: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
>> Cc: Guenter Roeck <linux at roeck-us.net>
>> Cc: linux-fbdev at vger.kernel.org
>> Cc: dri-devel at lists.freedesktop.org
>> Link: https://lore.kernel.org/all/YkHXO6LGHAN0p1pq@debian/ # [1]
>> ---
>> drivers/video/fbdev/core/fbmem.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
>> index 34d6bb1bf82e..a6bb0e438216 100644
>> --- a/drivers/video/fbdev/core/fbmem.c
>> +++ b/drivers/video/fbdev/core/fbmem.c
>> @@ -1579,7 +1579,14 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
>> * If it's not a platform device, at least print a warning. A
>> * fix would add code to remove the device from the system.
>> */
>> - if (dev_is_platform(device)) {
>> + if (!device) {
>> + /* TODO: Represent each OF framebuffer as its own
>> + * device in the device hierarchy. For now, offb
>> + * doesn't have such a device, so unregister the
>> + * framebuffer as before without warning.
>> + */
>> + do_unregister_framebuffer(registered_fb[i]);
>
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>
> Might be good to have a fb_info flag for offb and then check in
> register_framebuffer that everyone else does have a device? Just to make
> sure we don't have more surprises here ...
That exists already: all generic/firmware drivers are flagged with
FBINFO_MISC_FIRMWARE specifically for the purpose of unloading.
HW-native fbdev drivers don't have the flags and will never be unloaded.
I double-checked and of the generic drivers, (efifb, vesafb, offb,
simplefb, vga16) only offb had no device set.
Best regards
Thomas
> -Daniel
>
>
>> + } else if (dev_is_platform(device)) {
>> registered_fb[i]->forced_out = true;
>> platform_device_unregister(to_platform_device(device));
>> } else {
>> --
>> 2.35.1
>>
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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