The rcu_barrier() takes the cpu_hotplug mutex which itself is not
reclaim-safe, and so rcu_barrier() is illegal from inside the shrinker.

[  309.661373] =========================================================
[  309.661376] [ INFO: possible irq lock inversion dependency detected ]
[  309.661380] 4.11.0-rc1-CI-CI_DRM_2333+ #1 Tainted: G        W
[  309.661383] ---------------------------------------------------------
[  309.661386] gem_exec_gttfil/6435 just changed the state of lock:
[  309.661389]  (rcu_preempt_state.barrier_mutex){+.+.-.}, at: [<ffffffff81100731>] _rcu_barrier+0x31/0x160
[  309.661399] but this lock took another, RECLAIM_FS-unsafe lock in the past:
[  309.661402]  (cpu_hotplug.lock){+.+.+.}
[  309.661404]

               and interrupts could create inverse lock ordering between them.

[  309.661410]
               other info that might help us debug this:
[  309.661414]  Possible interrupt unsafe locking scenario:

[  309.661417]        CPU0                    CPU1
[  309.661419]        ----                    ----
[  309.661421]   lock(cpu_hotplug.lock);
[  309.661425]                                local_irq_disable();
[  309.661432]                                lock(rcu_preempt_state.barrier_mutex);
[  309.661441]                                lock(cpu_hotplug.lock);
[  309.661446]   <Interrupt>
[  309.661448]     lock(rcu_preempt_state.barrier_mutex);
[  309.661453]
                *** DEADLOCK ***

[  309.661460] 4 locks held by gem_exec_gttfil/6435:
[  309.661464]  #0:  (sb_writers#10){.+.+.+}, at: [<ffffffff8120d83d>] vfs_write+0x17d/0x1f0
[  309.661475]  #1:  (debugfs_srcu){......}, at: [<ffffffff81320491>] debugfs_use_file_start+0x41/0xa0
[  309.661486]  #2:  (&attr->mutex){+.+.+.}, at: [<ffffffff8123a3e7>] simple_attr_write+0x37/0xe0
[  309.661495]  #3:  (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa0091b4a>] i915_drop_caches_set+0x3a/0x150 [i915]
[  309.661540]
               the shortest dependencies between 2nd lock and 1st lock:
[  309.661547]  -> (cpu_hotplug.lock){+.+.+.} ops: 829 {
[  309.661553]     HARDIRQ-ON-W at:
[  309.661560]                       __lock_acquire+0x5e5/0x1b50
[  309.661565]                       lock_acquire+0xc9/0x220
[  309.661572]                       __mutex_lock+0x6e/0x990
[  309.661576]                       mutex_lock_nested+0x16/0x20
[  309.661583]                       get_online_cpus+0x61/0x80
[  309.661590]                       kmem_cache_create+0x25/0x1d0
[  309.661596]                       debug_objects_mem_init+0x30/0x249
[  309.661602]                       start_kernel+0x341/0x3fe
[  309.661607]                       x86_64_start_reservations+0x2a/0x2c
[  309.661612]                       x86_64_start_kernel+0x173/0x186
[  309.661619]                       verify_cpu+0x0/0xfc
[  309.661622]     SOFTIRQ-ON-W at:
[  309.661627]                       __lock_acquire+0x611/0x1b50
[  309.661632]                       lock_acquire+0xc9/0x220
[  309.661636]                       __mutex_lock+0x6e/0x990
[  309.661641]                       mutex_lock_nested+0x16/0x20
[  309.661646]                       get_online_cpus+0x61/0x80
[  309.661650]                       kmem_cache_create+0x25/0x1d0
[  309.661655]                       debug_objects_mem_init+0x30/0x249
[  309.661660]                       start_kernel+0x341/0x3fe
[  309.661664]                       x86_64_start_reservations+0x2a/0x2c
[  309.661669]                       x86_64_start_kernel+0x173/0x186
[  309.661674]                       verify_cpu+0x0/0xfc
[  309.661677]     RECLAIM_FS-ON-W at:
[  309.661682]                          mark_held_locks+0x6f/0xa0
[  309.661687]                          lockdep_trace_alloc+0xb3/0x100
[  309.661693]                          kmem_cache_alloc_trace+0x31/0x2e0
[  309.661699]                          __smpboot_create_thread.part.1+0x27/0xe0
[  309.661704]                          smpboot_create_threads+0x61/0x90
[  309.661709]                          cpuhp_invoke_callback+0x9c/0x8a0
[  309.661713]                          cpuhp_up_callbacks+0x31/0xb0
[  309.661718]                          _cpu_up+0x7a/0xc0
[  309.661723]                          do_cpu_up+0x5f/0x80
[  309.661727]                          cpu_up+0xe/0x10
[  309.661734]                          smp_init+0x71/0xb3
[  309.661738]                          kernel_init_freeable+0x94/0x19e
[  309.661743]                          kernel_init+0x9/0xf0
[  309.661748]                          ret_from_fork+0x2e/0x40
[  309.661752]     INITIAL USE at:
[  309.661757]                      __lock_acquire+0x234/0x1b50
[  309.661761]                      lock_acquire+0xc9/0x220
[  309.661766]                      __mutex_lock+0x6e/0x990
[  309.661771]                      mutex_lock_nested+0x16/0x20
[  309.661775]                      get_online_cpus+0x61/0x80
[  309.661780]                      __cpuhp_setup_state+0x44/0x170
[  309.661785]                      page_alloc_init+0x23/0x3a
[  309.661790]                      start_kernel+0x124/0x3fe
[  309.661794]                      x86_64_start_reservations+0x2a/0x2c
[  309.661799]                      x86_64_start_kernel+0x173/0x186
[  309.661804]                      verify_cpu+0x0/0xfc
[  309.661807]   }
[  309.661813]   ... key      at: [<ffffffff81e37690>] cpu_hotplug+0xb0/0x100
[  309.661817]   ... acquired at:
[  309.661821]    lock_acquire+0xc9/0x220
[  309.661825]    __mutex_lock+0x6e/0x990
[  309.661829]    mutex_lock_nested+0x16/0x20
[  309.661833]    get_online_cpus+0x61/0x80
[  309.661837]    _rcu_barrier+0x9f/0x160
[  309.661841]    rcu_barrier+0x10/0x20
[  309.661847]    netdev_run_todo+0x5f/0x310
[  309.661852]    rtnl_unlock+0x9/0x10
[  309.661856]    default_device_exit_batch+0x133/0x150
[  309.661862]    ops_exit_list.isra.0+0x4d/0x60
[  309.661866]    cleanup_net+0x1d8/0x2c0
[  309.661872]    process_one_work+0x1f4/0x6d0
[  309.661876]    worker_thread+0x49/0x4a0
[  309.661881]    kthread+0x107/0x140
[  309.661884]    ret_from_fork+0x2e/0x40

[  309.661890] -> (rcu_preempt_state.barrier_mutex){+.+.-.} ops: 179 {
[  309.661896]    HARDIRQ-ON-W at:
[  309.661901]                     __lock_acquire+0x5e5/0x1b50
[  309.661905]                     lock_acquire+0xc9/0x220
[  309.661910]                     __mutex_lock+0x6e/0x990
[  309.661914]                     mutex_lock_nested+0x16/0x20
[  309.661919]                     _rcu_barrier+0x31/0x160
[  309.661923]                     rcu_barrier+0x10/0x20
[  309.661928]                     netdev_run_todo+0x5f/0x310
[  309.661932]                     rtnl_unlock+0x9/0x10
[  309.661936]                     default_device_exit_batch+0x133/0x150
[  309.661941]                     ops_exit_list.isra.0+0x4d/0x60
[  309.661946]                     cleanup_net+0x1d8/0x2c0
[  309.661951]                     process_one_work+0x1f4/0x6d0
[  309.661955]                     worker_thread+0x49/0x4a0
[  309.661960]                     kthread+0x107/0x140
[  309.661964]                     ret_from_fork+0x2e/0x40
[  309.661968]    SOFTIRQ-ON-W at:
[  309.661972]                     __lock_acquire+0x611/0x1b50
[  309.661977]                     lock_acquire+0xc9/0x220
[  309.661981]                     __mutex_lock+0x6e/0x990
[  309.661986]                     mutex_lock_nested+0x16/0x20
[  309.661990]                     _rcu_barrier+0x31/0x160
[  309.661995]                     rcu_barrier+0x10/0x20
[  309.661999]                     netdev_run_todo+0x5f/0x310
[  309.662003]                     rtnl_unlock+0x9/0x10
[  309.662008]                     default_device_exit_batch+0x133/0x150
[  309.662013]                     ops_exit_list.isra.0+0x4d/0x60
[  309.662017]                     cleanup_net+0x1d8/0x2c0
[  309.662022]                     process_one_work+0x1f4/0x6d0
[  309.662027]                     worker_thread+0x49/0x4a0
[  309.662031]                     kthread+0x107/0x140
[  309.662035]                     ret_from_fork+0x2e/0x40
[  309.662039]    IN-RECLAIM_FS-W at:
[  309.662043]                        __lock_acquire+0x638/0x1b50
[  309.662048]                        lock_acquire+0xc9/0x220
[  309.662053]                        __mutex_lock+0x6e/0x990
[  309.662058]                        mutex_lock_nested+0x16/0x20
[  309.662062]                        _rcu_barrier+0x31/0x160
[  309.662067]                        rcu_barrier+0x10/0x20
[  309.662089]                        i915_gem_shrink_all+0x33/0x40 [i915]
[  309.662109]                        i915_drop_caches_set+0x141/0x150 [i915]
[  309.662114]                        simple_attr_write+0xc7/0xe0
[  309.662119]                        full_proxy_write+0x4f/0x70
[  309.662124]                        __vfs_write+0x23/0x120
[  309.662128]                        vfs_write+0xc6/0x1f0
[  309.662133]                        SyS_write+0x44/0xb0
[  309.662138]                        entry_SYSCALL_64_fastpath+0x1c/0xb1
[  309.662142]    INITIAL USE at:
[  309.662147]                    __lock_acquire+0x234/0x1b50
[  309.662151]                    lock_acquire+0xc9/0x220
[  309.662156]                    __mutex_lock+0x6e/0x990
[  309.662160]                    mutex_lock_nested+0x16/0x20
[  309.662165]                    _rcu_barrier+0x31/0x160
[  309.662169]                    rcu_barrier+0x10/0x20
[  309.662174]                    netdev_run_todo+0x5f/0x310
[  309.662178]                    rtnl_unlock+0x9/0x10
[  309.662183]                    default_device_exit_batch+0x133/0x150
[  309.662188]                    ops_exit_list.isra.0+0x4d/0x60
[  309.662192]                    cleanup_net+0x1d8/0x2c0
[  309.662197]                    process_one_work+0x1f4/0x6d0
[  309.662202]                    worker_thread+0x49/0x4a0
[  309.662206]                    kthread+0x107/0x140
[  309.662210]                    ret_from_fork+0x2e/0x40
[  309.662214]  }
[  309.662220]  ... key      at: [<ffffffff81e4e1c8>] rcu_preempt_state+0x508/0x780
[  309.662225]  ... acquired at:
[  309.662229]    check_usage_forwards+0x12b/0x130
[  309.662233]    mark_lock+0x360/0x6f0
[  309.662237]    __lock_acquire+0x638/0x1b50
[  309.662241]    lock_acquire+0xc9/0x220
[  309.662245]    __mutex_lock+0x6e/0x990
[  309.662249]    mutex_lock_nested+0x16/0x20
[  309.662253]    _rcu_barrier+0x31/0x160
[  309.662257]    rcu_barrier+0x10/0x20
[  309.662279]    i915_gem_shrink_all+0x33/0x40 [i915]
[  309.662298]    i915_drop_caches_set+0x141/0x150 [i915]
[  309.662303]    simple_attr_write+0xc7/0xe0
[  309.662307]    full_proxy_write+0x4f/0x70
[  309.662311]    __vfs_write+0x23/0x120
[  309.662315]    vfs_write+0xc6/0x1f0
[  309.662319]    SyS_write+0x44/0xb0
[  309.662323]    entry_SYSCALL_64_fastpath+0x1c/0xb1

[  309.662329]
               stack backtrace:
[  309.662335] CPU: 1 PID: 6435 Comm: gem_exec_gttfil Tainted: G        W       4.11.0-rc1-CI-CI_DRM_2333+ #1
[  309.662342] Hardware name: Hewlett-Packard HP Compaq 8100 Elite SFF PC/304Ah, BIOS 786H1 v01.13 07/14/2011
[  309.662348] Call Trace:
[  309.662354]  dump_stack+0x67/0x92
[  309.662359]  print_irq_inversion_bug.part.19+0x1a4/0x1b0
[  309.662365]  check_usage_forwards+0x12b/0x130
[  309.662369]  mark_lock+0x360/0x6f0
[  309.662374]  ? print_shortest_lock_dependencies+0x1a0/0x1a0
[  309.662379]  __lock_acquire+0x638/0x1b50
[  309.662383]  ? __mutex_unlock_slowpath+0x3e/0x2e0
[  309.662388]  ? trace_hardirqs_on+0xd/0x10
[  309.662392]  ? _rcu_barrier+0x31/0x160
[  309.662396]  lock_acquire+0xc9/0x220
[  309.662400]  ? _rcu_barrier+0x31/0x160
[  309.662404]  ? _rcu_barrier+0x31/0x160
[  309.662409]  __mutex_lock+0x6e/0x990
[  309.662412]  ? _rcu_barrier+0x31/0x160
[  309.662416]  ? _rcu_barrier+0x31/0x160
[  309.662421]  ? synchronize_rcu_expedited+0x35/0xb0
[  309.662426]  ? _raw_spin_unlock_irqrestore+0x52/0x60
[  309.662434]  mutex_lock_nested+0x16/0x20
[  309.662438]  _rcu_barrier+0x31/0x160
[  309.662442]  rcu_barrier+0x10/0x20
[  309.662464]  i915_gem_shrink_all+0x33/0x40 [i915]
[  309.662484]  i915_drop_caches_set+0x141/0x150 [i915]
[  309.662489]  simple_attr_write+0xc7/0xe0
[  309.662494]  full_proxy_write+0x4f/0x70
[  309.662498]  __vfs_write+0x23/0x120
[  309.662503]  ? rcu_read_lock_sched_held+0x75/0x80
[  309.662507]  ? rcu_sync_lockdep_assert+0x2a/0x50
[  309.662512]  ? __sb_start_write+0x102/0x210
[  309.662516]  ? vfs_write+0x17d/0x1f0
[  309.662520]  vfs_write+0xc6/0x1f0
[  309.662524]  ? trace_hardirqs_on_caller+0xe7/0x200
[  309.662529]  SyS_write+0x44/0xb0
[  309.662533]  entry_SYSCALL_64_fastpath+0x1c/0xb1
[  309.662537] RIP: 0033:0x7f507eac24a0
[  309.662541] RSP: 002b:00007fffda8720e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  309.662548] RAX: ffffffffffffffda RBX: ffffffff81482bd3 RCX: 00007f507eac24a0
[  309.662552] RDX: 0000000000000005 RSI: 00007fffda8720f0 RDI: 0000000000000005
[  309.662557] RBP: ffffc9000048bf88 R08: 0000000000000000 R09: 000000000000002c
[  309.662561] R10: 0000000000000014 R11: 0000000000000246 R12: 00007fffda872230
[  309.662566] R13: 00007fffda872228 R14: 0000000000000201 R15: 00007fffda8720f0
[  309.662572]  ? __this_cpu_preempt_check+0x13/0x20

Fixes: 0eafec6d ("drm/i915: Enable lockless lookup of request tracking via RCU")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100192Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # v4.9+
Link: http://patchwork.freedesktop.org/patch/msgid/20170314115019.18127-1-chris@chris-wilson.co.ukReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>