linux.git/arch/arm64/kernel/stacktrace.c, branch v4.11 Linux kernel source tree sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02T07:42:36+00:00 Ingo Molnar mingo@kernel.org 2017-02-08T17:51:37+00:00 68db0cf10678630d286f4bbbbdfa102951a35faa We are going to split <linux/sched/task_stack.h> out of <linux/sched.h>, which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder <linux/sched/task_stack.h> file that just maps to <linux/sched.h> to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> 
We are going to split <linux/sched/task_stack.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/task_stack.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
sched/headers: Prepare for new header dependencies before moving code to <linux/sched/debug.h> 2017-03-02T07:42:34+00:00 Ingo Molnar mingo@kernel.org 2017-02-08T17:51:35+00:00 b17b01533b719e9949e437abf66436a875739b40 We are going to split <linux/sched/debug.h> out of <linux/sched.h>, which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder <linux/sched/debug.h> file that just maps to <linux/sched.h> to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> 
We are going to split <linux/sched/debug.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/debug.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arm64: prep stack walkers for THREAD_INFO_IN_TASK 2016-11-11T18:25:44+00:00 Mark Rutland mark.rutland@arm.com 2016-11-03T20:23:08+00:00 9bbd4c56b0b642f04396da378296e68096d5afca When CONFIG_THREAD_INFO_IN_TASK is selected, task stacks may be freed before a task is destroyed. To account for this, the stacks are refcounted, and when manipulating the stack of another task, it is necessary to get/put the stack to ensure it isn't freed and/or re-used while we do so. This patch reworks the arm64 stack walking code to account for this. When CONFIG_THREAD_INFO_IN_TASK is not selected these perform no refcounting, and this should only be a structural change that does not affect behaviour. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Laura Abbott <labbott@redhat.com> Cc: AKASHI Takahiro <takahiro.akashi@linaro.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: James Morse <james.morse@arm.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> 
When CONFIG_THREAD_INFO_IN_TASK is selected, task stacks may be freed
before a task is destroyed. To account for this, the stacks are
refcounted, and when manipulating the stack of another task, it is
necessary to get/put the stack to ensure it isn't freed and/or re-used
while we do so.

This patch reworks the arm64 stack walking code to account for this.
When CONFIG_THREAD_INFO_IN_TASK is not selected these perform no
refcounting, and this should only be a structural change that does not
affect behaviour.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
arm64: unexport walk_stackframe 2016-11-11T18:25:43+00:00 Mark Rutland mark.rutland@arm.com 2016-11-03T20:23:07+00:00 2020a5ae7c8c2c8504565004915017507b135c63 The walk_stackframe functions is architecture-specific, with a varying prototype, and common code should not use it directly. None of its current users can be built as modules. With THREAD_INFO_IN_TASK, users will also need to hold a stack reference before calling it. There's no reason for it to be exported, and it's very easy to misuse, so unexport it for now. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> 
The walk_stackframe functions is architecture-specific, with a varying
prototype, and common code should not use it directly. None of its
current users can be built as modules. With THREAD_INFO_IN_TASK, users
will also need to hold a stack reference before calling it.

There's no reason for it to be exported, and it's very easy to misuse,
so unexport it for now.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
arm64: factor out current_stack_pointer 2016-11-11T18:25:43+00:00 Mark Rutland mark.rutland@arm.com 2016-11-03T20:23:05+00:00 a9ea0017ebe8889dfa136cac2aa7ae0ee6915e1f We define current_stack_pointer in <asm/thread_info.h>, though other files and header relying upon it do not have this necessary include, and are thus fragile to changes in the header soup. Subsequent patches will affect the header soup such that directly including <asm/thread_info.h> may result in a circular header include in some of these cases, so we can't simply include <asm/thread_info.h>. Instead, factor current_thread_info into its own header, and have all existing users include this explicitly. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Laura Abbott <labbott@redhat.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> 
We define current_stack_pointer in <asm/thread_info.h>, though other
files and header relying upon it do not have this necessary include, and
are thus fragile to changes in the header soup.

Subsequent patches will affect the header soup such that directly
including <asm/thread_info.h> may result in a circular header include in
some of these cases, so we can't simply include <asm/thread_info.h>.

Instead, factor current_thread_info into its own header, and have all
existing users include this explicitly.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
arm64: fix dump_backtrace/unwind_frame with NULL tsk 2016-09-26T13:24:01+00:00 Mark Rutland mark.rutland@arm.com 2016-09-23T16:55:05+00:00 b5e7307d9d5a340d2c9fabbe1cee137d4c682c71 In some places, dump_backtrace() is called with a NULL tsk parameter, e.g. in bug_handler() in arch/arm64, or indirectly via show_stack() in core code. The expectation is that this is treated as if current were passed instead of NULL. Similar is true of unwind_frame(). Commit a80a0eb70c358f8c ("arm64: make irq_stack_ptr more robust") didn't take this into account. In dump_backtrace() it compares tsk against current *before* we check if tsk is NULL, and in unwind_frame() we never set tsk if it is NULL. Due to this, we won't initialise irq_stack_ptr in either function. In dump_backtrace() this results in calling dump_mem() for memory immediately above the IRQ stack range, rather than for the relevant range on the task stack. In unwind_frame we'll reject unwinding frames on the IRQ stack. In either case this results in incomplete or misleading backtrace information, but is not otherwise problematic. The initial percpu areas (including the IRQ stacks) are allocated in the linear map, and dump_mem uses __get_user(), so we shouldn't access anything with side-effects, and will handle holes safely. This patch fixes the issue by having both functions handle the NULL tsk case before doing anything else with tsk. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Fixes: a80a0eb70c358f8c ("arm64: make irq_stack_ptr more robust") Acked-by: James Morse <james.morse@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Yang Shi <yang.shi@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> 
In some places, dump_backtrace() is called with a NULL tsk parameter,
e.g. in bug_handler() in arch/arm64, or indirectly via show_stack() in
core code. The expectation is that this is treated as if current were
passed instead of NULL. Similar is true of unwind_frame().

Commit a80a0eb70c358f8c ("arm64: make irq_stack_ptr more robust") didn't
take this into account. In dump_backtrace() it compares tsk against
current *before* we check if tsk is NULL, and in unwind_frame() we never
set tsk if it is NULL.

Due to this, we won't initialise irq_stack_ptr in either function. In
dump_backtrace() this results in calling dump_mem() for memory
immediately above the IRQ stack range, rather than for the relevant
range on the task stack. In unwind_frame we'll reject unwinding frames
on the IRQ stack.

In either case this results in incomplete or misleading backtrace
information, but is not otherwise problematic. The initial percpu areas
(including the IRQ stacks) are allocated in the linear map, and dump_mem
uses __get_user(), so we shouldn't access anything with side-effects,
and will handle holes safely.

This patch fixes the issue by having both functions handle the NULL tsk
case before doing anything else with tsk.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: a80a0eb70c358f8c ("arm64: make irq_stack_ptr more robust")
Acked-by: James Morse <james.morse@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yang Shi <yang.shi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arm64: ftrace: add save_stack_trace_regs() 2016-09-05T12:41:52+00:00 Pratyush Anand panand@redhat.com 2016-09-05T02:33:16+00:00 98ab10e9770e3ce9fbd263689644be9d81a06885 Currently, enabling stacktrace of a kprobe events generates warning: echo stacktrace > /sys/kernel/debug/tracing/trace_options echo "p xhci_irq" > /sys/kernel/debug/tracing/kprobe_events echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable save_stack_trace_regs() not implemented yet. ------------[ cut here ]------------ WARNING: CPU: 1 PID: 0 at ../kernel/stacktrace.c:74 save_stack_trace_regs+0x3c/0x48 Modules linked in: CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.8.0-rc4-dirty #5128 Hardware name: ARM Juno development board (r1) (DT) task: ffff800975dd1900 task.stack: ffff800975ddc000 PC is at save_stack_trace_regs+0x3c/0x48 LR is at save_stack_trace_regs+0x3c/0x48 pc : [<ffff000008126c64>] lr : [<ffff000008126c64>] pstate: 600003c5 sp : ffff80097ef52c00 Call trace: save_stack_trace_regs+0x3c/0x48 __ftrace_trace_stack+0x168/0x208 trace_buffer_unlock_commit_regs+0x5c/0x7c kprobe_trace_func+0x308/0x3d8 kprobe_dispatcher+0x58/0x60 kprobe_breakpoint_handler+0xbc/0x18c brk_handler+0x50/0x90 do_debug_exception+0x50/0xbc This patch implements save_stack_trace_regs(), so that stacktrace of a kprobe events can be obtained. After this patch, there is no warning and we can see the stacktrace for kprobe events in trace buffer. more /sys/kernel/debug/tracing/trace <idle>-0 [004] d.h. 1356.000496: p_xhci_irq_0:(xhci_irq+0x0/0x9ac) <idle>-0 [004] d.h. 1356.000497: <stack trace> => xhci_irq => __handle_irq_event_percpu => handle_irq_event_percpu => handle_irq_event => handle_fasteoi_irq => generic_handle_irq => __handle_domain_irq => gic_handle_irq => el1_irq => arch_cpu_idle => default_idle_call => cpu_startup_entry => secondary_start_kernel => Tested-by: David A. Long <dave.long@linaro.org> Reviewed-by: James Morse <james.morse@arm.com> Signed-off-by: Pratyush Anand <panand@redhat.com> Signed-off-by: Will Deacon <will.deacon@arm.com> 
Currently, enabling stacktrace of a kprobe events generates warning:

  echo stacktrace > /sys/kernel/debug/tracing/trace_options
  echo "p xhci_irq" > /sys/kernel/debug/tracing/kprobe_events
  echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable

save_stack_trace_regs() not implemented yet.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 0 at ../kernel/stacktrace.c:74 save_stack_trace_regs+0x3c/0x48
Modules linked in:

CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.8.0-rc4-dirty #5128
Hardware name: ARM Juno development board (r1) (DT)
task: ffff800975dd1900 task.stack: ffff800975ddc000
PC is at save_stack_trace_regs+0x3c/0x48
LR is at save_stack_trace_regs+0x3c/0x48
pc : [<ffff000008126c64>] lr : [<ffff000008126c64>] pstate: 600003c5
sp : ffff80097ef52c00

Call trace:
   save_stack_trace_regs+0x3c/0x48
   __ftrace_trace_stack+0x168/0x208
   trace_buffer_unlock_commit_regs+0x5c/0x7c
   kprobe_trace_func+0x308/0x3d8
   kprobe_dispatcher+0x58/0x60
   kprobe_breakpoint_handler+0xbc/0x18c
   brk_handler+0x50/0x90
   do_debug_exception+0x50/0xbc

This patch implements save_stack_trace_regs(), so that stacktrace of a
kprobe events can be obtained.

After this patch, there is no warning and we can see the stacktrace for
kprobe events in trace buffer.

more /sys/kernel/debug/tracing/trace
          <idle>-0     [004] d.h.  1356.000496: p_xhci_irq_0:(xhci_irq+0x0/0x9ac)
          <idle>-0     [004] d.h.  1356.000497: <stack trace>
  => xhci_irq
  => __handle_irq_event_percpu
  => handle_irq_event_percpu
  => handle_irq_event
  => handle_fasteoi_irq
  => generic_handle_irq
  => __handle_domain_irq
  => gic_handle_irq
  => el1_irq
  => arch_cpu_idle
  => default_idle_call
  => cpu_startup_entry
  => secondary_start_kernel
  =>

Tested-by: David A. Long <dave.long@linaro.org>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Pratyush Anand <panand@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arm64: make irq_stack_ptr more robust 2016-02-12T15:53:51+00:00 Yang Shi yang.shi@linaro.org 2016-02-11T21:53:10+00:00 a80a0eb70c358f8c7dda4bb62b2278dc6285217b Switching between stacks is only valid if we are tracing ourselves while on the irq_stack, so it is only valid when in current and non-preemptible context, otherwise is is just zeroed off. Fixes: 132cd887b5c5 ("arm64: Modify stack trace and dump for use with irq_stack") Acked-by: James Morse <james.morse@arm.com> Tested-by: James Morse <james.morse@arm.com> Signed-off-by: Yang Shi <yang.shi@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> 
Switching between stacks is only valid if we are tracing ourselves while on the
irq_stack, so it is only valid when in current and non-preemptible context,
otherwise is is just zeroed off.

Fixes: 132cd887b5c5 ("arm64: Modify stack trace and dump for use with irq_stack")
Acked-by: James Morse <james.morse@arm.com>
Tested-by: James Morse <james.morse@arm.com>
Signed-off-by: Yang Shi <yang.shi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arm64: disable kasan when accessing frame->fp in unwind_frame 2016-02-09T17:55:30+00:00 Yang Shi yang.shi@linaro.org 2016-02-08T17:13:09+00:00 bcaf669b4bdbad09888df086d266a34e293ace85 When boot arm64 kernel with KASAN enabled, the below error is reported by kasan: BUG: KASAN: out-of-bounds in unwind_frame+0xec/0x260 at addr ffffffc064d57ba0 Read of size 8 by task pidof/499 page:ffffffbdc39355c0 count:0 mapcount:0 mapping: (null) index:0x0 flags: 0x0() page dumped because: kasan: bad access detected CPU: 2 PID: 499 Comm: pidof Not tainted 4.5.0-rc1 #119 Hardware name: Freescale Layerscape 2085a RDB Board (DT) Call trace: [<ffffffc00008d078>] dump_backtrace+0x0/0x290 [<ffffffc00008d32c>] show_stack+0x24/0x30 [<ffffffc0006a981c>] dump_stack+0x8c/0xd8 [<ffffffc0002e4400>] kasan_report_error+0x558/0x588 [<ffffffc0002e4958>] kasan_report+0x60/0x70 [<ffffffc0002e3188>] __asan_load8+0x60/0x78 [<ffffffc00008c92c>] unwind_frame+0xec/0x260 [<ffffffc000087e60>] get_wchan+0x110/0x160 [<ffffffc0003b647c>] do_task_stat+0xb44/0xb68 [<ffffffc0003b7730>] proc_tgid_stat+0x40/0x50 [<ffffffc0003ac840>] proc_single_show+0x88/0xd8 [<ffffffc000345be8>] seq_read+0x370/0x770 [<ffffffc00030aba0>] __vfs_read+0xc8/0x1d8 [<ffffffc00030c0ec>] vfs_read+0x94/0x168 [<ffffffc00030d458>] SyS_read+0xb8/0x128 [<ffffffc000086530>] el0_svc_naked+0x24/0x28 Memory state around the buggy address: ffffffc064d57a80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 f4 f4 ffffffc064d57b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffffffc064d57b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ^ ffffffc064d57c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffffffc064d57c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 Since the shadow byte pointed by the report is 0, so it may mean it is just hit oob in non-current task. So, disable the instrumentation to silence these warnings. Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Signed-off-by: Yang Shi <yang.shi@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> 
When boot arm64 kernel with KASAN enabled, the below error is reported by
kasan:

BUG: KASAN: out-of-bounds in unwind_frame+0xec/0x260 at addr ffffffc064d57ba0
Read of size 8 by task pidof/499
page:ffffffbdc39355c0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x0()
page dumped because: kasan: bad access detected
CPU: 2 PID: 499 Comm: pidof Not tainted 4.5.0-rc1 #119
Hardware name: Freescale Layerscape 2085a RDB Board (DT)
Call trace:
[<ffffffc00008d078>] dump_backtrace+0x0/0x290
[<ffffffc00008d32c>] show_stack+0x24/0x30
[<ffffffc0006a981c>] dump_stack+0x8c/0xd8
[<ffffffc0002e4400>] kasan_report_error+0x558/0x588
[<ffffffc0002e4958>] kasan_report+0x60/0x70
[<ffffffc0002e3188>] __asan_load8+0x60/0x78
[<ffffffc00008c92c>] unwind_frame+0xec/0x260
[<ffffffc000087e60>] get_wchan+0x110/0x160
[<ffffffc0003b647c>] do_task_stat+0xb44/0xb68
[<ffffffc0003b7730>] proc_tgid_stat+0x40/0x50
[<ffffffc0003ac840>] proc_single_show+0x88/0xd8
[<ffffffc000345be8>] seq_read+0x370/0x770
[<ffffffc00030aba0>] __vfs_read+0xc8/0x1d8
[<ffffffc00030c0ec>] vfs_read+0x94/0x168
[<ffffffc00030d458>] SyS_read+0xb8/0x128
[<ffffffc000086530>] el0_svc_naked+0x24/0x28
Memory state around the buggy address:
 ffffffc064d57a80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 f4 f4
 ffffffc064d57b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffffc064d57b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                                  ^
 ffffffc064d57c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffffc064d57c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Since the shadow byte pointed by the report is 0, so it may mean it is just hit
oob in non-current task. So, disable the instrumentation to silence these
warnings.

Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Yang Shi <yang.shi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arm64: ftrace: fix a stack tracer's output under function graph tracer 2015-12-21T17:26:02+00:00 AKASHI Takahiro takahiro.akashi@linaro.org 2015-12-15T08:33:41+00:00 20380bb390a443b2c5c8800cec59743faf8151b4 Function graph tracer modifies a return address (LR) in a stack frame to hook a function return. This will result in many useless entries (return_to_handler) showing up in a) a stack tracer's output b) perf call graph (with perf record -g) c) dump_backtrace (at panic et al.) For example, in case of a), $ echo function_graph > /sys/kernel/debug/tracing/current_tracer $ echo 1 > /proc/sys/kernel/stack_trace_enabled $ cat /sys/kernel/debug/tracing/stack_trace Depth Size Location (54 entries) ----- ---- -------- 0) 4504 16 gic_raise_softirq+0x28/0x150 1) 4488 80 smp_cross_call+0x38/0xb8 2) 4408 48 return_to_handler+0x0/0x40 3) 4360 32 return_to_handler+0x0/0x40 ... In case of b), $ echo function_graph > /sys/kernel/debug/tracing/current_tracer $ perf record -e mem:XXX:x -ag -- sleep 10 $ perf report ... | | |--0.22%-- 0x550f8 | | | 0x10888 | | | el0_svc_naked | | | sys_openat | | | return_to_handler | | | return_to_handler ... In case of c), $ echo function_graph > /sys/kernel/debug/tracing/current_tracer $ echo c > /proc/sysrq-trigger ... Call trace: [<ffffffc00044d3ac>] sysrq_handle_crash+0x24/0x30 [<ffffffc000092250>] return_to_handler+0x0/0x40 [<ffffffc000092250>] return_to_handler+0x0/0x40 ... This patch replaces such entries with real addresses preserved in current->ret_stack[] at unwind_frame(). This way, we can cover all the cases. Reviewed-by: Jungseok Lee <jungseoklee85@gmail.com> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> [will: fixed minor context changes conflicting with irq stack bits] Signed-off-by: Will Deacon <will.deacon@arm.com> 
Function graph tracer modifies a return address (LR) in a stack frame
to hook a function return. This will result in many useless entries
(return_to_handler) showing up in
 a) a stack tracer's output
 b) perf call graph (with perf record -g)
 c) dump_backtrace (at panic et al.)

For example, in case of a),
  $ echo function_graph > /sys/kernel/debug/tracing/current_tracer
  $ echo 1 > /proc/sys/kernel/stack_trace_enabled
  $ cat /sys/kernel/debug/tracing/stack_trace
        Depth    Size   Location    (54 entries)
        -----    ----   --------
  0)     4504      16   gic_raise_softirq+0x28/0x150
  1)     4488      80   smp_cross_call+0x38/0xb8
  2)     4408      48   return_to_handler+0x0/0x40
  3)     4360      32   return_to_handler+0x0/0x40
  ...

In case of b),
  $ echo function_graph > /sys/kernel/debug/tracing/current_tracer
  $ perf record -e mem:XXX:x -ag -- sleep 10
  $ perf report
                  ...
                  |          |          |--0.22%-- 0x550f8
                  |          |          |          0x10888
                  |          |          |          el0_svc_naked
                  |          |          |          sys_openat
                  |          |          |          return_to_handler
                  |          |          |          return_to_handler
                  ...

In case of c),
  $ echo function_graph > /sys/kernel/debug/tracing/current_tracer
  $ echo c > /proc/sysrq-trigger
  ...
  Call trace:
  [<ffffffc00044d3ac>] sysrq_handle_crash+0x24/0x30
  [<ffffffc000092250>] return_to_handler+0x0/0x40
  [<ffffffc000092250>] return_to_handler+0x0/0x40
  ...

This patch replaces such entries with real addresses preserved in
current->ret_stack[] at unwind_frame(). This way, we can cover all
the cases.

Reviewed-by: Jungseok Lee <jungseoklee85@gmail.com>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
[will: fixed minor context changes conflicting with irq stack bits]
Signed-off-by: Will Deacon <will.deacon@arm.com>