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This patch prevents division by zero htotal. In a follow-up mail Tina writes: > > How did you manage to get here with htotal == 0? This needs backtraces (or if > > this is just about static checkers, a mention of that). > > -Daniel > > In GVT-g, we are trying to enable a virtual display w/o setting timings for a pipe > (a.k.a htotal=0), then we met the following kernel panic: > > [ 32.832048] divide error: 0000 [#1] SMP PTI > [ 32.833614] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc4-sriov+ #33 > [ 32.834438] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.10.1-0-g8891697-dirty-20180511_165818-tinazhang-linux-1 04/01/2014 > [ 32.835901] RIP: 0010:drm_mode_hsync+0x1e/0x40 > [ 32.836004] Code: 31 c0 c3 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 8b 87 d8 00 00 00 85 c0 75 22 8b 4f 68 85 c9 78 1b 69 47 58 e8 03 00 00 99 <f7> f9 b9 d3 4d 62 10 05 f4 01 00 00 f7 e1 89 d0 c1 e8 06 f3 c3 66 > [ 32.836004] RSP: 0000:ffffc900000ebb90 EFLAGS: 00010206 > [ 32.836004] RAX: 0000000000000000 RBX: ffff88001c67c8a0 RCX: 0000000000000000 > [ 32.836004] RDX: 0000000000000000 RSI: ffff88001c67c000 RDI: ffff88001c67c8a0 > [ 32.836004] RBP: ffff88001c7d03a0 R08: ffff88001c67c8a0 R09: ffff88001c7d0330 > [ 32.836004] R10: ffffffff822c3a98 R11: 0000000000000001 R12: ffff88001c67c000 > [ 32.836004] R13: ffff88001c7d0370 R14: ffffffff8207eb78 R15: ffff88001c67c800 > [ 32.836004] FS: 0000000000000000(0000) GS:ffff88001da00000(0000) knlGS:0000000000000000 > [ 32.836004] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 32.836004] CR2: 0000000000000000 CR3: 000000000220a000 CR4: 00000000000006f0 > [ 32.836004] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 32.836004] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 32.836004] Call Trace: > [ 32.836004] intel_mode_from_pipe_config+0x72/0x90 > [ 32.836004] intel_modeset_setup_hw_state+0x569/0xf90 > [ 32.836004] intel_modeset_init+0x905/0x1db0 > [ 32.836004] i915_driver_load+0xb8c/0x1120 > [ 32.836004] i915_pci_probe+0x4d/0xb0 > [ 32.836004] local_pci_probe+0x44/0xa0 > [ 32.836004] ? pci_assign_irq+0x27/0x130 > [ 32.836004] pci_device_probe+0x102/0x1c0 > [ 32.836004] driver_probe_device+0x2b8/0x480 > [ 32.836004] __driver_attach+0x109/0x110 > [ 32.836004] ? driver_probe_device+0x480/0x480 > [ 32.836004] bus_for_each_dev+0x67/0xc0 > [ 32.836004] ? klist_add_tail+0x3b/0x70 > [ 32.836004] bus_add_driver+0x1e8/0x260 > [ 32.836004] driver_register+0x5b/0xe0 > [ 32.836004] ? mipi_dsi_bus_init+0x11/0x11 > [ 32.836004] do_one_initcall+0x4d/0x1eb > [ 32.836004] kernel_init_freeable+0x197/0x237 > [ 32.836004] ? rest_init+0xd0/0xd0 > [ 32.836004] kernel_init+0xa/0x110 > [ 32.836004] ret_from_fork+0x35/0x40 > [ 32.836004] Modules linked in: > [ 32.859183] ---[ end trace 525608b0ed0e8665 ]--- > [ 32.859722] RIP: 0010:drm_mode_hsync+0x1e/0x40 > [ 32.860287] Code: 31 c0 c3 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 8b 87 d8 00 00 00 85 c0 75 22 8b 4f 68 85 c9 78 1b 69 47 58 e8 03 00 00 99 <f7> f9 b9 d3 4d 62 10 05 f4 01 00 00 f7 e1 89 d0 c1 e8 06 f3 c3 66 > [ 32.862680] RSP: 0000:ffffc900000ebb90 EFLAGS: 00010206 > [ 32.863309] RAX: 0000000000000000 RBX: ffff88001c67c8a0 RCX: 0000000000000000 > [ 32.864182] RDX: 0000000000000000 RSI: ffff88001c67c000 RDI: ffff88001c67c8a0 > [ 32.865206] RBP: ffff88001c7d03a0 R08: ffff88001c67c8a0 R09: ffff88001c7d0330 > [ 32.866359] R10: ffffffff822c3a98 R11: 0000000000000001 R12: ffff88001c67c000 > [ 32.867213] R13: ffff88001c7d0370 R14: ffffffff8207eb78 R15: ffff88001c67c800 > [ 32.868075] FS: 0000000000000000(0000) GS:ffff88001da00000(0000) knlGS:0000000000000000 > [ 32.868983] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 32.869659] CR2: 0000000000000000 CR3: 000000000220a000 CR4: 00000000000006f0 > [ 32.870599] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 32.871598] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 32.872549] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > > Since drm_mode_hsync() has the logic to check mode->htotal, I just extend it to cover the case htotal==0. Signed-off-by: Tina Zhang <tina.zhang@intel.com> Cc: Adam Jackson <ajax@redhat.com> Cc: Dave Airlie <airlied@redhat.com> Cc: Daniel Vetter <daniel@ffwll.ch> [danvet: Add additional explanations + cc: stable.] Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/1548228539-3061-1-git-send-email-tina.zhang@intel.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.