On Wed, Apr 03, 2019 at 04:35:11PM -0300, Rodrigo Siqueira wrote:
Hi,
I’m working to add writeback support to vkms; you can see my current patch at the end of this email (some prints highlight the issue that I’m asking for help here). I’m using the Liviu Dudau and Brian Starkey IGT patchset, which can be seen here: https://patchwork.freedesktop.org/series/39229/.
I’m stuck with a problem that happens in my vkms_wb_atomic_commit() function, which is a helper function at drm_connector_helper_funcs. You can see the full implementation of this function at the end of this email, but here is the important part:
struct drm_framebuffer *fb = conn_state->writeback_job->fb; struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0); struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(gem_obj);
A few lines after this variable initialization, I try to make a memory copy like this:
memcpy(vkms_conn->writeback_vaddr, vkms_obj->vaddr, vkms_obj->gem.size);
If I test my implementation with the subtest writeback-fb-id, everything work as expected; for extra details, this is the dmesg output after this test and with a debug print:
=> writeback-fb-id
[Apr 3 11:30] CIFS: Attempting to mount //10.0.2.4/qemu [ +1.601900] Console: switching to colour dummy device 80x25 [ +0.000017] [IGT] kms_writeback: executing [ +0.032532] [IGT] kms_writeback: starting subtest writeback-fb-id [ +0.001932] VKMS_OBJ (1): Buff (1) - Vaddr (1) - Size = 1228800 - count = 1 [ +0.050524] [IGT] kms_writeback: exiting, ret=0 [ +0.005202] Console: switching to colour frame buffer device 100x37
In the above log, you can see the print info; notice that Vaddr is the output of vkms_obj->vaddr (Vaddr -> vkms_obj->vaddr != NULL). On the other hand, if I try the subtest writeback-check-output, something weird happens in this function. Here is the dmesg output for this test:
=> writeback-check-output
[ +29.911185] Console: switching to colour dummy device 80x25 [ +0.000017] [IGT] kms_writeback: executing [ +0.021289] [IGT] kms_writeback: starting subtest writeback-check-output [ +0.016270] VKMS_OBJ (1): Buff (1) - Vaddr (0) - Size = 1228800 - count = 0 [ +0.000005] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 [ +0.000004] #PF error: [normal kernel read fault] [ +0.000001] PGD 0 P4D 0 [ +0.000003] Oops: 0000 [#1] PREEMPT SMP PTI [ +0.000002] CPU: 3 PID: 426 Comm: kms_writeback Not tainted 5.0.0-VKMS-RULES+ #102 [ +0.000002] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014 [ +0.000021] RIP: 0010:__memcpy+0x12/0x20 [ +0.000002] Code: ff 0f 31 48 c1 e2 20 48 09 c2 48 31 d3 e9 79 ff ff ff 90 90 90 90 90 90 0f 1f 44 00 00 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 f3 a4 [ +0.000001] RSP: 0018:ffffadaf0098fbd8 EFLAGS: 00010246 [ +0.000002] RAX: ffff9f1bf5400000 RBX: ffff9f1bfa28df00 RCX: 0000000000025800 [ +0.000001] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9f1bf5400000 [ +0.000001] RBP: 0000000000000001 R08: 00000017818788be R09: ffffadaf0098fb60 [ +0.000001] R10: ffff9f1bfffdc998 R11: ffffffffa25ec401 R12: ffff9f1b777ff430 [ +0.000001] R13: ffffffffc06558b8 R14: ffffffffc06853c0 R15: ffffffffc0685520 [ +0.000002] FS: 00007f2862deae80(0000) GS:ffff9f1bfc980000(0000) knlGS:0000000000000000 [ +0.000001] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ +0.000001] CR2: 0000000000000000 CR3: 00000000baf6c000 CR4: 00000000000006e0 [ +0.000004] Call Trace: [ +0.000023] drm_atomic_helper_commit_modeset_enables+0x15d/0x1e0 [drm_kms_helper] [ +0.000028] drm_atomic_helper_commit_tail+0x31/0x60 [drm_kms_helper] [ +0.000008] commit_tail+0x58/0x70 [drm_kms_helper] [ +0.000008] drm_atomic_helper_commit+0x103/0x110 [drm_kms_helper] [ +0.000040] drm_mode_atomic_ioctl+0x829/0x950 [drm] [ +0.000012] ? drm_atomic_set_property+0x960/0x960 [drm] [ +0.000029] drm_ioctl_kernel+0xb2/0xf0 [drm] [ +0.000011] drm_ioctl+0x25f/0x3f0 [drm] [ +0.000009] ? drm_atomic_set_property+0x960/0x960 [drm] [ +0.000004] ? n_tty_open+0xa0/0xa0 [ +0.000004] do_vfs_ioctl+0xa4/0x630 [ +0.000003] ksys_ioctl+0x60/0x90 [ +0.000003] ? ksys_write+0x4f/0xb0 [ +0.000002] __x64_sys_ioctl+0x16/0x20 [ +0.000003] do_syscall_64+0x5b/0x170 [ +0.000003] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ +0.000002] RIP: 0033:0x7f286677580b [ +0.000001] Code: 0f 1e fa 48 8b 05 55 b6 0c 00 64 c7 00 26 00 00 00 48 c7 c0 ff
Notice that Vaddr became NULL for some reason that I cannot understand.
Just missing the .prepare_writeback_job() hook?