When we fetch the hot regs and rewind to the nth caller, it
might happen that we dereference a frame pointer outside the
kernel stack boundaries, like in this example:

	perf_trace_sched_switch+0xd5/0x120
        schedule+0x6b5/0x860
        retint_careful+0xd/0x21

Since we directly dereference a userspace frame pointer here while
rewinding behind retint_careful, this may end up in a crash.

Fix this by simply using probe_kernel_address() when we rewind the
frame pointer.

This issue will have a much more proper fix in the next version of the
perf_arch_fetch_caller_regs() API that will only need to rewind to the
first caller.
Reported-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Tested-by: NEric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: David Miller <davem@davemloft.net>
Cc: Archs <linux-arch@vger.kernel.org>

When profiling a 32-bit process on a 64-bit kernel, callgraph tracing
stopped after the first function, because it has seen a garbage memory
address (tried to interpret the frame pointer, and return address as a
64-bit pointer).

Fix this by using a struct stack_frame with 32-bit pointers when the
TIF_IA32 flag is set.

Note that TIF_IA32 flag must be used, and not is_compat_task(), because
the latter is only set when the 32-bit process is executing a syscall,
which may not always be the case (when tracing page fault events for
example).
Signed-off-by: NTörök Edwin <edwintorok@gmail.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
LKML-Reference: <1268820436-13145-1-git-send-email-edwintorok@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Events that trigger overflows by interrupting a context can
use get_irq_regs() or task_pt_regs() to retrieve the state
when the event triggered. But this is not the case for some
other class of events like trace events as tracepoints are
executed in the same context than the code that triggered
the event.

It means we need a different api to capture the regs there,
namely we need a hot snapshot to get the most important
informations for perf: the instruction pointer to get the
event origin, the frame pointer for the callchain, the code
segment for user_mode() tests (we always use __KERNEL_CS as
trace events always occur from the kernel) and the eflags
for further purposes.

v2: rename perf_save_regs to perf_fetch_caller_regs as per
Masami's suggestion.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Archs <linux-arch@vger.kernel.org>

The current print_context_stack helper that does the stack
walking job is good for usual stacktraces as it walks through
all the stack and reports even addresses that look unreliable,
which is nice when we don't have frame pointers for example.

But we have users like perf that only require reliable
stacktraces, and those may want a more adapted stack walker, so
lets make this function a callback in stacktrace_ops that users
can tune for their needs.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1261024834-5336-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

asm/stacktrace.h is more appropriate so removing other 2 declarations.
Signed-off-by: NJaswinder Singh Rajput <jaswinderrajput@gmail.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
LKML-Reference: <1239695308.3033.34.camel@ht.satnam>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: better dumpstack output

I noticed in my crash dumps and even in the stack tracer that a
lot of functions listed in the stack trace are simply
return_to_handler which is ftrace graphs way to insert its own
call into the return of a function.

But we lose out where the actually function was called from.

This patch adds in hooks to the dumpstack mechanism that detects
this and finds the real function to print. Both are printed to
let the user know that a hook is still in place.

This does give a funny side effect in the stack tracer output:

        Depth   Size      Location    (80 entries)
        -----   ----      --------
  0)     4144      48   save_stack_trace+0x2f/0x4d
  1)     4096     128   ftrace_call+0x5/0x2b
  2)     3968      16   mempool_alloc_slab+0x16/0x18
  3)     3952     384   return_to_handler+0x0/0x73
  4)     3568    -240   stack_trace_call+0x11d/0x209
  5)     3808     144   return_to_handler+0x0/0x73
  6)     3664    -128   mempool_alloc+0x4d/0xfe
  7)     3792     128   return_to_handler+0x0/0x73
  8)     3664     -32   scsi_sg_alloc+0x48/0x4a [scsi_mod]

As you can see, the real functions are now negative. This is due
to them not being found inside the stack.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Impact: cleanup

As promised, now that dumpstack_32 and dumpstack_64 have so many bits
in common, we should merge the in-sync bits into a common file, to
prevent them from diverging again.

This patch removes bits which are common between dumpstack_32.c and
dumpstack_64.c and places them in a common dumpstack.c which is built
for both 32 and 64 bit arches.
Signed-off-by: NNeil Horman <nhorman@tuxdriver.com>
Acked-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

 Makefile       |    2
 arch/x86/kernel/Makefile       |    2
 arch/x86/kernel/Makefile       |    2
 arch/x86/kernel/Makefile       |    2
 arch/x86/kernel/Makefile       |    2
 arch/x86/kernel/Makefile       |    2
 arch/x86/kernel/dumpstack.c    |  319 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/dumpstack.h    |   39 +++++
 arch/x86/kernel/dumpstack_32.c |  294 -------------------------------------
 arch/x86/kernel/dumpstack_64.c |  285 ------------------------------------
 5 files changed, 363 insertions(+), 576 deletions(-)