drm/i915: Use static allocation for i915_globals_park()

In order to avoid the malloc inside i915_globals_park() occurring
underneath a lock connected to the shrinker (thus causing circular
lockdeps warnings), move the rcu_worker to a global.

<4> [39.085073] ======================================================
<4> [39.085273] WARNING: possible circular locking dependency detected
<4> [39.085552] 5.1.0-rc3-CI-Trybot_4088+ #1 Tainted: G     U
<4> [39.085752] ------------------------------------------------------
<4> [39.085949] kswapd0/32 is trying to acquire lock:
<4> [39.086121] 00000000004b5f91 (wakeref#3){+.+.}, at: intel_engine_pm_put+0x1b/0x40 [i915]
<4> [39.086493]
but task is already holding lock:
<4> [39.086682] 00000000dd009a9a (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30
<4> [39.086910]
which lock already depends on the new lock.

<4> [39.087139]
the existing dependency chain (in reverse order) is:
<4> [39.087356]
-> #2 (fs_reclaim){+.+.}:
<4> [39.087604]        fs_reclaim_acquire.part.24+0x24/0x30
<4> [39.087785]        kmem_cache_alloc_trace+0x2a/0x290
<4> [39.087998]        i915_globals_park+0x22/0xa0 [i915]
<4> [39.088478]        idle_work_handler+0x1df/0x220 [i915]
<4> [39.089016]        process_one_work+0x245/0x610
<4> [39.089447]        worker_thread+0x37/0x380
<4> [39.089956]        kthread+0x119/0x130
<4> [39.090374]        ret_from_fork+0x3a/0x50
<4> [39.090868]
-> #1 (wakeref#4){+.+.}:
<4> [39.091569]        __mutex_lock+0x8c/0x960
<4> [39.092054]        atomic_dec_and_mutex_lock+0x33/0x50
<4> [39.092521]        intel_gt_pm_put+0x1b/0x40 [i915]
<4> [39.093047]        intel_engine_park+0xeb/0x1d0 [i915]
<4> [39.093514]        __intel_wakeref_put_once+0x10/0x30 [i915]
<4> [39.094062]        i915_request_retire+0x477/0xaf0 [i915]
<4> [39.094547]        ring_retire_requests+0x86/0x160 [i915]
<4> [39.095110]        i915_retire_requests+0x58/0xc0 [i915]
<4> [39.095587]        i915_gem_wait_for_idle.part.22+0xb2/0xf0 [i915]
<4> [39.096142]        switch_to_kernel_context_sync+0x2a/0x70 [i915]
<4> [39.096633]        i915_gem_init+0x59c/0x9c0 [i915]
<4> [39.097174]        i915_driver_load+0xd96/0x1880 [i915]
<4> [39.097640]        i915_pci_probe+0x29/0xa0 [i915]
<4> [39.098145]        pci_device_probe+0xa1/0x120
<4> [39.098607]        really_probe+0xf3/0x3e0
<4> [39.099031]        driver_probe_device+0x10a/0x120
<4> [39.099599]        device_driver_attach+0x4b/0x50
<4> [39.100033]        __driver_attach+0x97/0x130
<4> [39.100525]        bus_for_each_dev+0x74/0xc0
<4> [39.100954]        bus_add_driver+0x13f/0x210
<4> [39.101441]        driver_register+0x56/0xe0
<4> [39.101891]        do_one_initcall+0x58/0x2e0
<4> [39.102319]        do_init_module+0x56/0x1ea
<4> [39.102805]        load_module+0x2701/0x29e0
<4> [39.103231]        __se_sys_finit_module+0xd3/0xf0
<4> [39.103727]        do_syscall_64+0x55/0x190
<4> [39.104153]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4> [39.104736]
-> #0 (wakeref#3){+.+.}:
<4> [39.105437]        lock_acquire+0xa6/0x1c0
<4> [39.105923]        __mutex_lock+0x8c/0x960
<4> [39.106345]        atomic_dec_and_mutex_lock+0x33/0x50
<4> [39.106897]        intel_engine_pm_put+0x1b/0x40 [i915]
<4> [39.107375]        i915_request_retire+0x477/0xaf0 [i915]
<4> [39.107930]        ring_retire_requests+0x86/0x160 [i915]
<4> [39.108412]        i915_retire_requests+0x58/0xc0 [i915]
<4> [39.108934]        i915_gem_shrink+0xd8/0x5b0 [i915]
<4> [39.109431]        i915_gem_shrinker_scan+0x59/0x130 [i915]
<4> [39.109884]        do_shrink_slab+0x131/0x3e0
<4> [39.110380]        shrink_slab+0x228/0x2c0
<4> [39.110810]        shrink_node+0x177/0x460
<4> [39.111317]        balance_pgdat+0x239/0x580
<4> [39.111743]        kswapd+0x186/0x570
<4> [39.112221]        kthread+0x119/0x130
<4> [39.112641]        ret_from_fork+0x3a/0x50
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190408091728.20207-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_globals.c

@@ -17,6 +17,33 @@
 
 static LIST_HEAD(globals);
 
+static atomic_t active;
+static atomic_t epoch;
+static struct park_work {
+	struct rcu_work work;
+	int epoch;
+} park;
+
+static void i915_globals_shrink(void)
+{
+	struct i915_global *global;
+
+	/*
+	 * kmem_cache_shrink() discards empty slabs and reorders partially
+	 * filled slabs to prioritise allocating from the mostly full slabs,
+	 * with the aim of reducing fragmentation.
+	 */
+	list_for_each_entry(global, &globals, link)
+		global->shrink();
+}
+
+static void __i915_globals_park(struct work_struct *work)
+{
+	/* Confirm nothing woke up in the last grace period */
+	if (park.epoch == atomic_read(&epoch))
+		i915_globals_shrink();
+}
+
 void __init i915_global_register(struct i915_global *global)
 {
 	GEM_BUG_ON(!global->shrink);
@@ -57,44 +84,12 @@ int __init i915_globals_init(void)
 		}
 	}
 
+	INIT_RCU_WORK(&park.work, __i915_globals_park);
 	return 0;
 }
 
-static void i915_globals_shrink(void)
-{
-	struct i915_global *global;
-
-	/*
-	 * kmem_cache_shrink() discards empty slabs and reorders partially
-	 * filled slabs to prioritise allocating from the mostly full slabs,
-	 * with the aim of reducing fragmentation.
-	 */
-	list_for_each_entry(global, &globals, link)
-		global->shrink();
-}
-
-static atomic_t active;
-static atomic_t epoch;
-struct park_work {
-	struct rcu_work work;
-	int epoch;
-};
-
-static void __i915_globals_park(struct work_struct *work)
-{
-	struct park_work *wrk = container_of(work, typeof(*wrk), work.work);
-
-	/* Confirm nothing woke up in the last grace period */
-	if (wrk->epoch == atomic_read(&epoch))
-		i915_globals_shrink();
-
-	kfree(wrk);
-}
-
 void i915_globals_park(void)
 {
-	struct park_work *wrk;
-
 	/*
 	 * Defer shrinking the global slab caches (and other work) until
 	 * after a RCU grace period has completed with no activity. This
@@ -107,13 +102,8 @@ void i915_globals_park(void)
 	if (!atomic_dec_and_test(&active))
 		return;
 
-	wrk = kmalloc(sizeof(*wrk), GFP_KERNEL);
-	if (!wrk)
-		return;
-
-	wrk->epoch = atomic_inc_return(&epoch);
-	INIT_RCU_WORK(&wrk->work, __i915_globals_park);
-	queue_rcu_work(system_wq, &wrk->work);
+	park.epoch = atomic_inc_return(&epoch);
+	queue_rcu_work(system_wq, &park.work);
 }
 
 void i915_globals_unpark(void)
@@ -125,8 +115,8 @@ void i915_globals_unpark(void)
 void __exit i915_globals_exit(void)
 {
 	/* Flush any residual park_work */
-	rcu_barrier();
-	flush_scheduled_work();
+	atomic_inc(&epoch);
+	flush_rcu_work(&park.work);
 
 	__i915_globals_cleanup();