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We have seen a case of a bad reference count for vblanks with the Rockchip VOP: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 383 at drivers/gpu/drm/drm_irq.c:1198 drm_vblank_put+0x40/0xcc Modules linked in: brcmfmac brcmutil CPU: 1 PID: 383 Comm: kworker/u8:2 Not tainted 4.9.75-rt60 #1 Hardware name: Rockchip (Device Tree) Workqueue: events_unbound flip_worker Backtrace: [<c010b7b0>] (dump_backtrace) from [<c010ba4c>] (show_stack+0x18/0x1c) r7:c0b1b13c r6:600b0013 r5:00000000 r4:c0b1b13c [<c010ba34>] (show_stack) from [<c032d248>] (dump_stack+0x78/0x94) [<c032d1d0>] (dump_stack) from [<c011e6e8>] (__warn+0xe4/0x104) r7:00000009 r6:c03cf26c r5:00000000 r4:00000000 [<c011e604>] (__warn) from [<c011e7c0>] (warn_slowpath_null+0x28/0x30) r9:eeb443a0 r8:eeb443c8 r7:ee8a5ec0 r6:ee8a5ec0 r5:edb47f00 r4:ee096200 [<c011e798>] (warn_slowpath_null) from [<c03cf26c>] (drm_vblank_put+0x40/0xcc) [<c03cf22c>] (drm_vblank_put) from [<c03cf310>] (drm_crtc_vblank_put+0x18/0x1c) r5:edb47f00 r4:ee3c8a80 [<c03cf2f8>] (drm_crtc_vblank_put) from [<c03ef9b4>] (vop_fb_unref_worker+0x18/0x24) [<c03ef99c>] (vop_fb_unref_worker) from [<c03df194>] (flip_worker+0x98/0xb4) r5:edb47f00 r4:eeb443a8 [<c03df0fc>] (flip_worker) from [<c0134808>] (process_one_work+0x1a8/0x2fc) r9:00000000 r8:ee807d00 r7:00000000 r6:ee809c00 r5:eeb443a8 r4:edfe5f80 [<c0134660>] (process_one_work) from [<c01358ec>] (worker_thread+0x2ac/0x458) r10:00000088 r9:edfe5f98 r8:ee809c2c r7:c0b04100 r6:ee809c00 r5:ee809c00 r4:edfe5f80 [<c0135640>] (worker_thread) from [<c013a0bc>] (kthread+0xfc/0x10c) r10:00000000 r9:00000000 r8:c0135640 r7:edfe5f80 r6:00000000 r5:edf0e240 r4:ee8a4000 r3:ed194e00 [<c0139fc0>] (kthread) from [<c0107cb8>] (ret_from_fork+0x14/0x3c) r8:00000000 r7:00000000 r6:00000000 r5:c0139fc0 r4:edf0e240 ---[ end trace 0000000000000002 ]--- It seems that this is caused by unfortunate timing between vop_crtc_atomic_flush() and vop_handle_vblank() given the following ordering: atomic_flush handle_vblank ------------ ------------- drm_flip_work_queue set_bit if (test_and_clear_bit(...)) drm_flip_work_commit drm_vblank_get This results in vop_fb_unref_worker (called as flip work) decrementing the vblank refcount before it has been incremented. Signed-off-by: John Keeping <john@metanate.com> Reviewed-by: Sandy huang <hjc@rock-chips.com> Signed-off-by: Sandy Huang <hjc@rock-chips.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180328160351.23763-1-john@metanate.com
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.