• Chris Wilson's avatar
    drm/i915: Avoid calling i915_gem_object_unbind holding object lock · 8b1c78e0
    Chris Wilson authored
    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/728Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Reviewed-by: default avatarAndi Shyti <andi.shyti@intel.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20191206105527.1130413-5-chris@chris-wilson.co.uk
    8b1c78e0
intel_overlay.c 36.3 KB