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@xxxxxxx> Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal") Reported-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx> Cc: Zack Rusin <zackr@xxxxxxxxxx> Cc: Javier Martinez Canillas <javierm@xxxxxxxxxx> Cc: Hans de Goede <hdegoede@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # v5.11+ Cc: Helge Deller <deller@xxxxxx> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> Cc: Sam Ravnborg <sam@xxxxxxxxxxxx> Cc: Zheyu Ma <zheyuma97@xxxxxxxxx> Cc: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx> Cc: Zhen Lei <thunder.leizhen@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Alex Deucher <alexander.deucher@xxxxxxx> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Cc: Guenter Roeck <linux@xxxxxxxxxxxx> Cc: linux-fbdev@xxxxxxxxxxxxxxx Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx 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@xxxxxxxx> 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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