arm64: stacktrace: avoid listing stacktrace functions in stacktrace

arm64: stacktrace: avoid listing stacktrace functions in stacktrace

The stacktraces always begin as follows:

  [<c00117b4>] save_stack_trace_tsk+0x0/0x98
  [<c0011870>] save_stack_trace+0x24/0x28
  ...

This is because the stack trace code includes the stack frames for
itself.  This is incorrect behaviour, and also leads to "skip" doing the
wrong thing (which is the number of stack frames to avoid recording.)

Perversely, it does the right thing when passed a non-current thread.
Fix this by ensuring that we have a known constant number of frames
above the main stack trace function, and always skip these.

This was fixed for arch arm by commit 0ceb38933d45 ("ARM: stacktrace:
avoid listing stacktrace functions in stacktrace")

Link: http://lkml.kernel.org/r/1504078343-28754-1-git-send-email-guptap@codeaurora.org
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>