aef8207992
All pinning must be done prior to i915_request_create, to avoid timeline->mutex inversions. Here we slightly abuse the context_barrier_task stages to utilise the 'skip' decision as an opportunity to acquire the pin on the new ppgtt. Consider it s/skip/prepare/. At the moment, we only have on user of context_barrier_task, so it might be worth breaking it down for the specific task of set-vm and refactor it later if we find a second purpose. <4> [402.377487] WARNING: possible circular locking dependency detected <4> [402.377493] 5.4.0-rc8-CI-CI_DRM_7491+ #1 Tainted: G U <4> [402.377497] ------------------------------------------------------ <4> [402.377502] gem_exec_parall/2506 is trying to acquire lock: <4> [402.377507] ffff888403cdac70 (&kernel#2){+.+.}, at: i915_request_create+0x16/0x1c0 [i915] <4> [402.377593] but task is already holding lock: <4> [402.377597] ffff88835efad550 (&ppgtt->pin_mutex){+.+.}, at: gen6_ppgtt_pin+0x4d/0x110 [i915] <4> [402.377660] which lock already depends on the new lock. <4> [402.377664] the existing dependency chain (in reverse order) is: <4> [402.377668] -> #1 (&ppgtt->pin_mutex){+.+.}: <4> [402.377674] __mutex_lock+0x9a/0x9d0 <4> [402.377713] gen6_ppgtt_pin+0x4d/0x110 [i915] <4> [402.377756] emit_ppgtt_update+0x1dc/0x370 [i915] <4> [402.377801] context_barrier_task+0x176/0x310 [i915] <4> [402.377844] ctx_setparam+0x400/0xb10 [i915] <4> [402.377886] i915_gem_context_setparam_ioctl+0xc8/0x160 [i915] <4> [402.377891] drm_ioctl_kernel+0xa7/0xf0 <4> [402.377895] drm_ioctl+0x2e1/0x390 <4> [402.377899] do_vfs_ioctl+0xa0/0x6f0 <4> [402.377903] ksys_ioctl+0x35/0x60 <4> [402.377906] __x64_sys_ioctl+0x11/0x20 <4> [402.377910] do_syscall_64+0x4f/0x210 <4> [402.377914] entry_SYSCALL_64_after_hwframe+0x49/0xbe <4> [402.377917] -> #0 (&kernel#2){+.+.}: <4> [402.377923] __lock_acquire+0x1328/0x15d0 <4> [402.377926] lock_acquire+0xa7/0x1c0 <4> [402.377930] __mutex_lock+0x9a/0x9d0 <4> [402.377977] i915_request_create+0x16/0x1c0 [i915] <4> [402.378013] intel_engine_flush_barriers+0x4c/0x100 [i915] <4> [402.378062] i915_ggtt_pin+0x7d/0x130 [i915] <4> [402.378108] gen6_ppgtt_pin+0x9c/0x110 [i915] <4> [402.378148] ring_context_pin+0x2e/0xc0 [i915] <4> [402.378183] __intel_context_do_pin+0x6b/0x190 [i915] <4> [402.378226] i915_gem_do_execbuffer+0x180c/0x26b0 [i915] <4> [402.378268] i915_gem_execbuffer2_ioctl+0x11b/0x460 [i915] <4> [402.378272] drm_ioctl_kernel+0xa7/0xf0 <4> [402.378275] drm_ioctl+0x2e1/0x390 <4> [402.378279] do_vfs_ioctl+0xa0/0x6f0 <4> [402.378282] ksys_ioctl+0x35/0x60 <4> [402.378286] __x64_sys_ioctl+0x11/0x20 <4> [402.378289] do_syscall_64+0x4f/0x210 <4> [402.378292] entry_SYSCALL_64_after_hwframe+0x49/0xbe <4> [402.378295] other info that might help us debug this: <4> [402.378299] Possible unsafe locking scenario: <4> [402.378302] CPU0 CPU1 <4> [402.378305] ---- ---- <4> [402.378307] lock(&ppgtt->pin_mutex); <4> [402.378310] lock(&kernel#2); <4> [402.378314] lock(&ppgtt->pin_mutex); <4> [402.378317] lock(&kernel#2); <4> [402.378320] Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Andi Shyti <andi.shyti@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191206105527.1130413-4-chris@chris-wilson.co.uk
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
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.