coresight: etm_perf: Fix using uninitialised work

With 4.11-rc4, the following command triggers a WARN_ON,
when a sink is not enabled.

 perf record -e cs_etm/@20010000.etf/

 [88286.547741] ------------[ cut here ]------------
 [88286.552332] WARNING: CPU: 3 PID: 2156 at kernel/workqueue.c:1442 __queue_work+0x29c/0x3b8
 [88286.560427] Modules linked in:
 [88286.563451]
 [88286.564928] CPU: 3 PID: 2156 Comm: perf_v4.11 Not tainted 4.11.0-rc4 #217
 [88286.573453] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Aug 15
  2016
 [88286.584128] task: ffff80097597c200 task.stack: ffff8009768b0000
 [88286.589990] PC is at __queue_work+0x29c/0x3b8
 [88286.594303] LR is at __queue_work+0x104/0x3b8
 [88286.598614] pc : [<ffff0000080d8c7c>] lr : [<ffff0000080d8ae4>] pstate: a00001c5
 [88286.605934] sp : ffff8009768b3aa0
 [88286.609212] x29: ffff8009768b3aa0 x28: ffff80097ff3da00
 [88286.614477] x27: ffff80097ff89c00 x26: ffff8009751b0e00
 [88286.619741] x25: ffff000008c9f000 x24: 0000000000000003
 [88286.625004] x23: 0000000000000040 x22: ffff000008d3dab8
 [88286.630268] x21: ffff800977804400 x20: 0000000000000007
 [88286.635532] x19: ffff000008c54000 x18: 0000fffff9185160
 [88286.640795] x17: 0000ffffb33d9a38 x16: ffff000008088270
 [88286.646059] x15: 0000ffffb345b590 x14: 0000000000000000
 [88286.651322] x13: 0000000000000004 x12: 0000000000000040
 [88286.656586] x11: 0000000000000068 x10: 0000000000000000
 [88286.661849] x9 : ffff800977400028 x8 : 0000000000000000
 [88286.667113] x7 : 0000000000000000 x6 : ffff0000080d8ae4
 [88286.672376] x5 : 0000000000000000 x4 : 0000000000000080
 [88286.677639] x3 : 0000000000000000 x2 : 0000000000000000
 [88286.682903] x1 : 0000000000000000 x0 : ffff8009751b0e08
 [88286.688166]
 [88286.689638] ---[ end trace 31633f18fd33d4cb ]---
 [88286.694206] Call trace:
 [88286.696627] Exception stack(0xffff8009768b38d0 to 0xffff8009768b3a00)
 [88286.703004] 38c0:                                   ffff000008c54000 0001000000000000
 [88286.710757] 38e0: ffff8009768b3aa0 ffff0000080d8c7c ffff8009768b3b50 ffff80097ff8a5b0
 [88286.718511] 3900: 0000800977325000 0000000000000000 0000000000000040 ffff80097ffc6180
 [88286.726264] 3920: ffff8009768b3940 ffff0000088a8694 ffff80097ffc5800 0000000000000000
 [88286.734017] 3940: ffff8009768b3960 ffff0000081919c0 ffff80097ffc5280 0000000000000001
 [88286.741771] 3960: ffff8009768b3a50 ffff00000819206c ffff8009751b0e08 0000000000000000
 [88286.749523] 3980: 0000000000000000 0000000000000000 0000000000000080 0000000000000000
 [88286.757277] 39a0: ffff0000080d8ae4 0000000000000000 0000000000000000 ffff800977400028
 [88286.765029] 39c0: 0000000000000000 0000000000000068 0000000000000040 0000000000000004
 [88286.772783] 39e0: 0000000000000000 0000ffffb345b590 ffff000008088270 0000ffffb33d9a38
 [88286.780537] [<ffff0000080d8c7c>] __queue_work+0x29c/0x3b8
 [88286.785883] [<ffff0000080d8df8>] queue_work_on+0x60/0x78
 [88286.791146] [<ffff000008764c68>] etm_setup_aux+0x178/0x238
 [88286.796578] [<ffff000008183600>] rb_alloc_aux+0x228/0x310
 [88286.801925] [<ffff00000817e564>] perf_mmap+0x404/0x5a8
 [88286.807015] [<ffff0000081c60cc>] mmap_region+0x394/0x5c0
 [88286.812276] [<ffff0000081c654c>] do_mmap+0x254/0x388
 [88286.817191] [<ffff0000081a989c>] vm_mmap_pgoff+0xbc/0xe0
 [88286.822452] [<ffff0000081c3ffc>] SyS_mmap_pgoff+0xac/0x228
 [88286.827884] [<ffff000008088288>] sys_mmap+0x18/0x28
 [88286.832714] [<ffff000008082f30>] el0_svc_naked+0x24/0x28

The patch makes sure that the event_data->work is initialised
properly before we could possibly use it.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm-perf.c

@@ -201,6 +201,7 @@ static void *etm_setup_aux(int event_cpu, void **pages,
 	event_data = alloc_event_data(event_cpu);
 	if (!event_data)
 		return NULL;
+	INIT_WORK(&event_data->work, free_event_data);
 
 	/*
 	 * In theory nothing prevent tracers in a trace session from being
@@ -217,8 +218,6 @@ static void *etm_setup_aux(int event_cpu, void **pages,
 	if (!sink)
 		goto err;
 
-	INIT_WORK(&event_data->work, free_event_data);
-
 	mask = &event_data->mask;
 
 	/* Setup the path for each CPU in a trace session */