Rabin Vincent reports:
| On SMP, this BUG() in save_stack_trace_tsk() can be easily triggered
| from user space by reading /proc/$PID/stack, where $PID is any pid but
| the current process:
|
|	if (tsk != current) {
| #ifdef CONFIG_SMP
|		/*
|		 * What guarantees do we have here that 'tsk'
|		 * is not running on another CPU?
|		 */
|		BUG();
| #else

Fix this by replacing the BUG() with an entry to terminate the stack
trace, returning an empty trace - I'd rather not expose the dwarf
unwinder to a volatile stack of a running thread.

Reported-by: Rabin Vincent <rabin@rab.in>
Tested-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

When unwinding stack frames we must take care not to unwind
areas of memory that lie outside of the known extent of the stack.

This patch fixes an incorrect calculation of the stack base where
THREAD_SIZE is added to the stack pointer after it has already
been aligned to this value. Since the ALIGN macro performs this
addition internally, we end up overshooting the base by 8k.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

As __builtin_return_address(n) doesn't work for ARM with n > 0, the
kernel needs its own implementation.

This fixes many warnings saying:

	warning: unsupported argument to '__builtin_return_address'

The new methods and walk_stackframe must not be instrumented because
CALLER_ADDRESSx is used in the various tracers and tracing the tracer is
a bad idea.

What's currently missing is an implementation using unwind tables.  This
is not fatal though, it's just that the tracers don't get enough
information to be really useful.

Note that if both ARM_UNWIND and FRAME_POINTER are enabled,
walk_stackframe uses unwind information.  So in this case the same
implementation is used as when FRAME_POINTER is disabled.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

This patch changes the walk_stacktrace and its callers for easier
integration of stack unwinding. The arch/arm/kernel/stacktrace.h file is
also moved to arch/arm/include/asm/stacktrace.h.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

* 'core/stacktrace' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  generic-ipi: powerpc/generic-ipi tree build failure
  stacktrace: fix build failure on sparc64
  stacktrace: export save_stack_trace[_tsk]
  stacktrace: fix modular build, export print_stack_trace and save_stack_trace
  backtrace: replace timer with tasklet + completions
  stacktrace: add saved stack traces to backtrace self-test
  stacktrace: print_stack_trace() cleanup
  debugging: make stacktrace independent from DEBUG_KERNEL
  stacktrace: don't crash on invalid stack trace structs

Andrew Morton reported this against linux-next:

ERROR: ".save_stack_trace" [tests/backtracetest.ko] undefined!

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Available for !SMP only at the moment.

From Russell:

|Basically, if a thread is running on a CPU, thread_saved_fp() is invalid.
|So, the question is: what guarantees do we have here that 'tsk' is not
|running on another CPU?

Signed-off-by: Nicolas Pitre <nico@marvell.com>
Tested-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>

Fix an oops in the stacktrace code, caused by improper range checking.
We subtract 12 off 'fp' before testing to see if it's below the low
bound.  However, if 'fp' were zero before, it becomes a very large
positive number, causing this test to succeed where it should fail.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

oprofile depends on having it

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ab1b6f03a10ba1f5638188ab06bf46e33ac3a160 said

 - remove the unused task argument to save_stack_trace, it's always current

then broke arm:

arch/arm/kernel/stacktrace.c:56: error: conflicting types for 'save_stack_trace'
include/linux/stacktrace.h:11: error: previous declaration of 'save_stack_trace' was here
arch/arm/kernel/stacktrace.c:56: error: conflicting types for 'save_stack_trace'
include/linux/stacktrace.h:11: error: previous declaration of 'save_stack_trace' was here

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>