On Tue, Dec 17, 2024 at 12:43:11PM +0100, Thomas Zimmermann wrote: > (cc'ing Hans, who implemented deferred console takeover) > > Hi > > Am 16.12.24 um 18:35 schrieb Dr. David Alan Gilbert: > > * Thomas Zimmermann (tzimmermann@xxxxxxx) wrote: > > > Hi > > > > > > > > > Am 16.12.24 um 14:46 schrieb Dr. David Alan Gilbert: > > > [...] > > > > > The attached patch fixes the problem for me. Could you please test and > > > > > report back the results. > > > > That gets me a different oops; this was run with: > > > > qemu-system-x86_64 -M pc -cpu host --enable-kvm -smp 4 -m 2G -kernel /discs/fast/kernel/arch/x86/boot/bzImage -append "console=tty0 console=ttyS0 root=/dev/vdb1 single" -drive if=virtio,file=/discs/more/images/debian12-64scan.qcow2 > > > > > > > > It looks to me if it made the mistake of trying to print something in the middle of being removed: > > > From the stack trace below, I'd say it is the one at [1]. But I fail to > > > reproduce the problem. > > > > > > Could you please send me the complete output of dmesg after the system > > > finished booting? > > Sure; this is as far as it gets until it hits the vga oops that stops it: > > I was able to reproduce it a single time. My setup is > > - CONFIG_DEBUG_TEST_DRIVER_REMOVE=y > - CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER=y > - startup with vgacon > - 'quiet' on kernel command line (important!) > > and then I got the segfault you report. > > With the provided stack trace and log, I think I got some idea what is > happened > > > > > [ 0.000000][ T0] Linux version 6.13.0-rc2+ (dg@dalek) (gcc (GCC) 14.2.1 20240912 (Red Hat 14.2.1-3), GNU ld version 2.43.1-4.fc41) #373 SMP PREEMPT_DYNAMIC Mon Dec 16 13:25:32 GMT 2024 > > [ 0.000000][ T0] Command line: console=tty0 console=ttyS0 root=/dev/vdb1 single > [...] > > [ 74.077481][ T1] SPI driver abt-y030xx067a has no spi_device_id for abt,y030xx067a > > [ 74.088805][ T1] SPI driver panel-ilitek-ili9322 has no spi_device_id for dlink,dir-685-panel > > [ 74.090492][ T1] SPI driver panel-ilitek-ili9322 has no spi_device_id for ilitek,ili9322 > > [ 74.094556][ T1] SPI driver panel-innolux-ej030na has no spi_device_id for innolux,ej030na > > [ 74.106367][ T1] SPI driver nt39016 has no spi_device_id for kingdisplay,kd035g6-54nt > > [ 74.116623][ T1] SPI driver s6d27a1-panel has no spi_device_id for samsung,s6d27a1 > > [ 74.120701][ T1] SPI driver panel-samsung-s6e63m0 has no spi_device_id for samsung,s6e63m0 > > > [ 74.177273][ T1] bochs-drm 0000:00:02.0: vgaarb: deactivate vga console > > This comes from the first iteration in really_probe() [1]. This is the bochs > instance that will be removed. It should install fbcon, but that gets > deferred. I don't think that's correct, because ... > [1] https://elixir.bootlin.com/linux/v6.12.5/source/drivers/base/dd.c#L631 > > > [ 74.179388][ T1] [drm] Found bochs VGA, ID 0xb0c5. > > [ 74.180931][ T1] [drm] Framebuffer size 16384 kB @ 0xfd000000, mmio @ 0xfebf0000. > > [ 74.199314][ T1] [drm] Initialized bochs-drm 1.0.0 for 0000:00:02.0 on minor 2 > > [ 74.265834][ T1] fbcon: bochs-drmdrmfb (fb1) is primary device > > [ 74.265882][ T1] fbcon: Remapping primary device, fb1, to tty 1-63 ... the above line I think is only ever printed if we're not deferred anymore: - One such printk is in fbcon_remap_all(), but after checking for deferred_takeover and bailing out if that's set. - The other is in do_fb_registered -> fbcon_select_primary (but only if CONFIG_FRAMEBUFFER_DETECT_PRIMARY is set), which is before we check for deferred_takeover. But if deferred_takeover is set that path should print pr_info("fbcon: Deferring console take-over\n"); which does not seem to be the case. But then I have no idea why deferred fbcon could have any impact at all. Really puzzling. -Sima > > [ 79.736367][ T1] bochs-drm 0000:00:02.0: [drm] fb1: bochs-drmdrmfb frame buffer device > > End of first bochs instance here.. > > > [ 79.800872][ T1] bochs-drm 0000:00:02.0: vgaarb: deactivate vga console > > The second instance of bochs starts here and tries to deactivate the console > a second time. Notice that we didn't have any "Console is " or "Taking over > console" messages. > > > [ 79.802400][ T1] BUG: kernel NULL pointer dereference, address: 000000000000020c > > I've not been able to figure out what is a offset 0x20c (524 decimal). None > of the structs involved appears to have any fields starting at this offset. > The nearest case is vc_hi_font_mask, [2] which is at +520. Could be related > to aligned memory access. get_color() would read that field. [3] vc_num at > +512 is another candidate. > > [2] https://elixir.bootlin.com/linux/v6.13-rc2/source/include/linux/console_struct.h#L124 > [3] https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/video/fbdev/core/fbcon.c#L302 > > > [ 79.802448][ T1] #PF: supervisor write access in kernel mode > > [ 79.802498][ T1] #PF: error_code(0x0002) - not-present page > > [ 79.802545][ T1] PGD 0 P4D 0 > > [ 79.802622][ T1] Oops: Oops: 0002 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI > > [ 79.802669][ T1] CPU: 2 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W N 6.13.0-rc2+ #373 5a5c0ce8f09b0b72067981f01985e201a0118bb6 > > [ 79.802669][ T1] Tainted: [W]=WARN, [N]=TEST > > [ 79.802669][ T1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014 > > [ 79.802669][ T1] RIP: 0010:fbcon_cursor+0xa9/0x3c0 > > [ 79.802669][ T1] Code: c0 05 00 00 66 89 44 24 06 e8 f3 35 2a fd 0f b7 bb c0 05 00 00 e8 27 b8 e9 fc 49 8d bc 24 0c 02 00 00 49 89 c7 e8 d7 3d 2a fd <45> 89 bc 24 0c 02 00 00 48 8d bd e0 05 00 00 e8 c3 3b 2a fd 44 8b > > [ 79.802669][ T1] RSP: 0018:ffffb70f800136c0 EFLAGS: 00010046 > > [ 79.802669][ T1] RAX: 0000000000000000 RBX: ffff9d4fc10a8800 RCX: 0000000000000000 > > [ 79.802669][ T1] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 > > [ 79.802669][ T1] RBP: ffff9d4fc54ba800 R08: 0000000000000000 R09: 0000000000000000 > > [ 79.802669][ T1] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > > [ 79.802669][ T1] R13: 0000000000000000 R14: ffff9d4fc54bade8 R15: 0000000000000032 > > [ 79.802669][ T1] FS: 0000000000000000(0000) GS:ffff9d503d200000(0000) knlGS:0000000000000000 > > [ 79.802669][ T1] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 79.802669][ T1] CR2: 000000000000020c CR3: 0000000056520000 CR4: 0000000000350ef0 > > [ 79.802669][ T1] Call Trace: > > [ 79.802669][ T1] <TASK> > > [ 79.802669][ T1] ? __die+0x23/0x80 > > [ 79.802669][ T1] ? page_fault_oops+0x21c/0x240 > > [ 79.802669][ T1] ? do_user_addr_fault+0x893/0x1180 > > [ 79.802669][ T1] ? srso_return_thunk+0x5/0x7f > > [ 79.802669][ T1] ? exc_page_fault+0x3f/0x180 > > [ 79.802669][ T1] ? exc_page_fault+0x87/0x180 > > [ 79.802669][ T1] ? asm_exc_page_fault+0x26/0x40 > > > [ 79.802669][ T1] ? fbcon_cursor+0xa9/0x3c0 > > [ 79.802669][ T1] hide_cursor+0x66/0x1c0 > > [ 79.802669][ T1] vt_console_print+0x9b1/0xa40 > > I think we get here via steps [4] to [8]. > > [4] > https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/pci/vgaarb.c#L173 > [5] > https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/tty/vt/vt.c#L3287 > [6] > https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/tty/vt/vt.c#L861 > [7] > https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/tty/vt/vt.c#L846 > [8] https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/video/fbdev/core/fbcon.c#L1322 > > When vt_console_print() invokes the call at [9], it apparently replaces the > deferred console implementation (maybe ?) and > then the next line [5] operates on a NULL pointer somewhere. > > [9] > https://elixir.bootlin.com/linux/v6.13-rc2/source/drivers/tty/vt/vt.c#L3286 > > Best regards > Thomas > > > -- > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Software Solutions Germany GmbH > Frankenstrasse 146, 90461 Nuernberg, Germany > GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman > HRB 36809 (AG Nuernberg) > -- Simona Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
