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 3683f44c ("ARM: stacktrace:
avoid listing stacktrace functions in stacktrace")

Change-Id: I1a65ee011f022227204b406bb0288828a7beb0b8
Link: http://lkml.kernel.org/r/1504078343-28754-1-git-send-email-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: Stephen Rothwell <sfr@canb.auug.org.au>
Git-commit: 457b9ab50babff7100fe7902d195069561bc1db7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


[guptap@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>