8b1c78e06e
In the extreme case, we may wish to wait on an rcu-barrier to reap stale vm to purge the last of the object bindings. However, we are not allowed to use rcu_barrier() beneath the dma_resv (i.e. object) lock and do not take lightly the prospect of unlocking a mutex deep in the bowels of the routine. i915_gem_object_unbind() itself does not need the object lock, and it turns out the callers do not need to the unbind as part of a locked sequence around set-cache-level, so rearrange the code to avoid taking the object lock in the callers. <4> [186.816311] ====================================================== <4> [186.816313] WARNING: possible circular locking dependency detected <4> [186.816316] 5.4.0-rc8-CI-CI_DRM_7486+ #1 Tainted: G U <4> [186.816318] ------------------------------------------------------ <4> [186.816320] perf_pmu/1321 is trying to acquire lock: <4> [186.816322] ffff88849487c4d8 (&mm->mmap_sem#2){++++}, at: __might_fault+0x39/0x90 <4> [186.816331] but task is already holding lock: <4> [186.816333] ffffe8ffffa05008 (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0xa9/0x1b0 <4> [186.816339] which lock already depends on the new lock. <4> [186.816341] the existing dependency chain (in reverse order) is: <4> [186.816343] -> #6 (&cpuctx_mutex){+.+.}: <4> [186.816349] __mutex_lock+0x9a/0x9d0 <4> [186.816352] perf_event_init_cpu+0xa4/0x140 <4> [186.816357] perf_event_init+0x19d/0x1cd <4> [186.816362] start_kernel+0x372/0x4f4 <4> [186.816365] secondary_startup_64+0xa4/0xb0 <4> [186.816381] -> #5 (pmus_lock){+.+.}: <4> [186.816385] __mutex_lock+0x9a/0x9d0 <4> [186.816387] perf_event_init_cpu+0x6b/0x140 <4> [186.816404] cpuhp_invoke_callback+0x9b/0x9d0 <4> [186.816406] _cpu_up+0xa2/0x140 <4> [186.816409] do_cpu_up+0x61/0xa0 <4> [186.816411] smp_init+0x57/0x96 <4> [186.816413] kernel_init_freeable+0xac/0x1c7 <4> [186.816416] kernel_init+0x5/0x100 <4> [186.816419] ret_from_fork+0x24/0x50 <4> [186.816421] -> #4 (cpu_hotplug_lock.rw_sem){++++}: <4> [186.816424] cpus_read_lock+0x34/0xd0 <4> [186.816427] rcu_barrier+0xaa/0x190 <4> [186.816429] kernel_init+0x21/0x100 <4> [186.816431] ret_from_fork+0x24/0x50 <4> [186.816433] -> #3 (rcu_state.barrier_mutex){+.+.}: <4> [186.816436] __mutex_lock+0x9a/0x9d0 <4> [186.816438] rcu_barrier+0x23/0x190 <4> [186.816502] i915_gem_object_unbind+0x3a6/0x400 [i915] <4> [186.816537] i915_gem_object_set_cache_level+0x32/0x90 [i915] <4> [186.816571] i915_gem_object_pin_to_display_plane+0x5d/0x160 [i915] <4> [186.816612] intel_pin_and_fence_fb_obj+0x9e/0x200 [i915] <4> [186.816679] intel_plane_pin_fb+0x3f/0xd0 [i915] <4> [186.816717] intel_prepare_plane_fb+0x130/0x520 [i915] <4> [186.816722] drm_atomic_helper_prepare_planes+0x85/0x110 <4> [186.816761] intel_atomic_commit+0xc6/0x350 [i915] <4> [186.816764] drm_atomic_helper_update_plane+0xed/0x110 <4> [186.816768] setplane_internal+0x97/0x190 <4> [186.816770] drm_mode_setplane+0xcd/0x190 <4> [186.816773] drm_ioctl_kernel+0xa7/0xf0 <4> [186.816775] drm_ioctl+0x2e1/0x390 <4> [186.816778] do_vfs_ioctl+0xa0/0x6f0 <4> [186.816780] ksys_ioctl+0x35/0x60 <4> [186.816782] __x64_sys_ioctl+0x11/0x20 <4> [186.816785] do_syscall_64+0x4f/0x210 <4> [186.816787] entry_SYSCALL_64_after_hwframe+0x49/0xbe <4> [186.816789] -> #2 (reservation_ww_class_mutex){+.+.}: <4> [186.816793] __ww_mutex_lock.constprop.15+0xc3/0x1090 <4> [186.816795] ww_mutex_lock+0x39/0x70 <4> [186.816798] dma_resv_lockdep+0x10e/0x1f7 <4> [186.816800] do_one_initcall+0x58/0x2ff <4> [186.816802] kernel_init_freeable+0x137/0x1c7 <4> [186.816804] kernel_init+0x5/0x100 <4> [186.816806] ret_from_fork+0x24/0x50 <4> [186.816808] -> #1 (reservation_ww_class_acquire){+.+.}: <4> [186.816811] dma_resv_lockdep+0xec/0x1f7 <4> [186.816813] do_one_initcall+0x58/0x2ff <4> [186.816815] kernel_init_freeable+0x137/0x1c7 <4> [186.816817] kernel_init+0x5/0x100 <4> [186.816819] ret_from_fork+0x24/0x50 <4> [186.816820] -> #0 (&mm->mmap_sem#2){++++}: <4> [186.816824] __lock_acquire+0x1328/0x15d0 <4> [186.816826] lock_acquire+0xa7/0x1c0 <4> [186.816828] __might_fault+0x63/0x90 <4> [186.816831] _copy_to_user+0x1e/0x80 <4> [186.816834] perf_read+0x200/0x2b0 <4> [186.816836] vfs_read+0x96/0x160 <4> [186.816838] ksys_read+0x9f/0xe0 <4> [186.816839] do_syscall_64+0x4f/0x210 <4> [186.816841] entry_SYSCALL_64_after_hwframe+0x49/0xbe <4> [186.816843] other info that might help us debug this: <4> [186.816846] Chain exists of: &mm->mmap_sem#2 --> pmus_lock --> &cpuctx_mutex <4> [186.816849] Possible unsafe locking scenario: <4> [186.816851] CPU0 CPU1 <4> [186.816853] ---- ---- <4> [186.816854] lock(&cpuctx_mutex); <4> [186.816856] lock(pmus_lock); <4> [186.816858] lock(&cpuctx_mutex); <4> [186.816860] lock(&mm->mmap_sem#2); <4> [186.816861] *** DEADLOCK *** Closes: https://gitlab.freedesktop.org/drm/intel/issues/728 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/20191206105527.1130413-5-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.