[PATCH] coresight: fix kernel panic caused by invalid CPU

From: Wang Nan
Date: Mon Dec 26 2016 - 01:33:24 EST

Commit d52c9750f150 ("coresight: reset 'enable_sink' flag when need be")
caused a kernel panic because of the using of an invalid value: after
'for_each_cpu(cpu, mask)', value of local variable 'cpu' become invalid,
causes following 'cpu_to_node' access invalid memory area.

This patch brings the deleted 'cpu = cpumask_first(mask)' back.

Panic log:

$ perf record -e cs_etm// ls

Unable to handle kernel paging request at virtual address fffe801804af4f10
pgd = ffff8017ce031600
[fffe801804af4f10] *pgd=0000000000000000, *pud=0000000000000000
Internal error: Oops: 96000004 [#1] SMP
Modules linked in:
CPU: 33 PID: 1619 Comm: perf Not tainted 4.7.1+ #16
Hardware name: Huawei Taishan 2280 /CH05TEVBA, BIOS 1.10 11/24/2016
task: ffff8017cb0c8400 ti: ffff8017cb154000 task.ti: ffff8017cb154000
PC is at tmc_alloc_etf_buffer+0x60/0xd4
LR is at tmc_alloc_etf_buffer+0x44/0xd4
pc : [<ffff000008633df8>] lr : [<ffff000008633ddc>] pstate: 60000145
sp : ffff8017cb157b40
x29: ffff8017cb157b40 x28: 0000000000000000
7a60: ffff000008c64dc8 0000000000000006 0000000000000253 ffffffffffffffff
7a80: 0000000000000000 0000000000000000 ffff0000080872cc 0000000000000001
[<ffff000008633df8>] tmc_alloc_etf_buffer+0x60/0xd4
[<ffff000008632b9c>] etm_setup_aux+0x1dc/0x1e8
[<ffff00000816eed4>] rb_alloc_aux+0x2b0/0x338
[<ffff00000816a5e4>] perf_mmap+0x414/0x568
[<ffff0000081ab694>] mmap_region+0x324/0x544
[<ffff0000081abbe8>] do_mmap+0x334/0x3e0
[<ffff000008191150>] vm_mmap_pgoff+0xa4/0xc8
[<ffff0000081a9a30>] SyS_mmap_pgoff+0xb0/0x22c
[<ffff0000080872e4>] sys_mmap+0x18/0x28
[<ffff0000080843f0>] el0_svc_naked+0x24/0x28
Code: 912040a5 d0001c00 f873d821 911c6000 (b8656822)
---[ end trace 98933da8f92b0c9a ]---

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Xia Kaixu <xiakaixu@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
drivers/hwtracing/coresight/coresight-etm-perf.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 1774196..26cfac3 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -242,6 +242,7 @@ static void *etm_setup_aux(int event_cpu, void **pages,
if (!sink_ops(sink)->alloc_buffer)
goto err;

+ cpu = cpumask_first(mask);
/* Get the AUX specific data from the sink buffer */
event_data->snk_config =
sink_ops(sink)->alloc_buffer(sink, cpu, pages,