When we to enable the SMB by perf, the perf sched will call perf_ctx_lock()
to close system preempt in event_function_call(). But SMB::enable_smb() use
mutex to lock the critical section, which may sleep.

 BUG: sleeping function called from invalid context at kernel/locking/mutex.c:580
 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 153023, name: perf
 preempt_count: 2, expected: 0
 RCU nest depth: 0, expected: 0
 INFO: lockdep is turned off.
 irq event stamp: 0
 hardirqs last  enabled at (0): [<0000000000000000>] 0x0
 hardirqs last disabled at (0): [<ffffa2983f5c5f40>] copy_process+0xae8/0x2b48
 softirqs last  enabled at (0): [<ffffa2983f5c5f40>] copy_process+0xae8/0x2b48
 softirqs last disabled at (0): [<0000000000000000>] 0x0
 CPU: 2 PID: 153023 Comm: perf Kdump: loaded Tainted: G   W  O   6.5.0-rc4+ #1

 Call trace:
 ...
  __mutex_lock+0xbc/0xa70
  mutex_lock_nested+0x34/0x48
  smb_update_buffer+0x58/0x360 [ultrasoc_smb]
  etm_event_stop+0x204/0x2d8 [coresight]
  etm_event_del+0x1c/0x30 [coresight]
  event_sched_out+0x17c/0x3b8
  group_sched_out.part.0+0x5c/0x208
  __perf_event_disable+0x15c/0x210
  event_function+0xe0/0x230
  remote_function+0xb4/0xe8
  generic_exec_single+0x160/0x268
  smp_call_function_single+0x20c/0x2a0
  event_function_call+0x20c/0x220
  _perf_event_disable+0x5c/0x90
  perf_event_for_each_child+0x58/0xc0
  _perf_ioctl+0x34c/0x1250
  perf_ioctl+0x64/0x98
 ...

Use spinlock to replace mutex to control driver data access to one at a
time. The function copy_to_user() may sleep, it cannot be in a spinlock
context, so we can't simply replace it in smb_read(). But we can ensure
that only one user gets the SMB device fd by smb_open(), so remove the
locks from smb_read() and buffer synchronization is guaranteed by the user.

Fixes: 06f5c292 ("drivers/coresight: Add UltraSoc System Memory Buffer driver")
Signed-off-by: Junhao He <hejunhao3@huawei.com>
Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20231114133346.30489-2-hejunhao3@huawei.com