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 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 >> Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal") >> Reported-by: Sudip Mukherjee >> Cc: Zack Rusin >> Cc: Javier Martinez Canillas >> Cc: Hans de Goede >> Cc: stable@vger.kernel.org # v5.11+ >> Cc: Helge Deller >> Cc: Daniel Vetter >> Cc: Sam Ravnborg >> Cc: Zheyu Ma >> Cc: Xiyu Yang >> Cc: Zhen Lei >> Cc: Matthew Wilcox >> Cc: Alex Deucher >> Cc: Tetsuo Handa >> Cc: Guenter Roeck >> Cc: linux-fbdev@vger.kernel.org >> Cc: dri-devel@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 > > 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