linux-stable.git/arch/powerpc/kernel/stacktrace.c, branch v4.19.232

powerpc/stacktrace: Include linux/delay.h

2021-09-22T09:48:01+00:00

[ Upstream commit a6cae77f1bc89368a4e2822afcddc45c3062d499 ]

commit 7c6986ade69e ("powerpc/stacktrace: Fix spurious "stale" traces in raise_backtrace_ipi()")
introduces udelay() call without including the linux/delay.h header.
This may happen to work on master but the header that declares the
functionshould be included nonetheless.

Fixes: 7c6986ade69e ("powerpc/stacktrace: Fix spurious "stale" traces in raise_backtrace_ipi()")
Signed-off-by: Michal Suchanek 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210729180103.15578-1-msuchanek@suse.de
Signed-off-by: Sasha Levin

powerpc/stacktrace: Fix spurious "stale" traces in raise_backtrace_ipi()

2021-07-20T14:15:42+00:00

commit 7c6986ade69e3c81bac831645bc72109cd798a80 upstream.

In raise_backtrace_ipi() we iterate through the cpumask of CPUs, sending
each an IPI asking them to do a backtrace, but we don't wait for the
backtrace to happen.

We then iterate through the CPU mask again, and if any CPU hasn't done
the backtrace and cleared itself from the mask, we print a trace on its
behalf, noting that the trace may be "stale".

This works well enough when a CPU is not responding, because in that
case it doesn't receive the IPI and the sending CPU is left to print the
trace. But when all CPUs are responding we are left with a race between
the sending and receiving CPUs, if the sending CPU wins the race then it
will erroneously print a trace.

This leads to spurious "stale" traces from the sending CPU, which can
then be interleaved messily with the receiving CPU, note the CPU
numbers, eg:

  [ 1658.929157][    C7] rcu: Stack dump where RCU GP kthread last ran:
  [ 1658.929223][    C7] Sending NMI from CPU 7 to CPUs 1:
  [ 1658.929303][    C1] NMI backtrace for cpu 1
  [ 1658.929303][    C7] CPU 1 didn't respond to backtrace IPI, inspecting paca.
  [ 1658.929362][    C1] CPU: 1 PID: 325 Comm: kworker/1:1H Tainted: G        W   E     5.13.0-rc2+ #46
  [ 1658.929405][    C7] irq_soft_mask: 0x01 in_mce: 0 in_nmi: 0 current: 325 (kworker/1:1H)
  [ 1658.929465][    C1] Workqueue: events_highpri test_work_fn [test_lockup]
  [ 1658.929549][    C7] Back trace of paca->saved_r1 (0xc0000000057fb400) (possibly stale):
  [ 1658.929592][    C1] NIP:  c00000000002cf50 LR: c008000000820178 CTR: c00000000002cfa0

To fix it, change the logic so that the sending CPU waits 5s for the
receiving CPU to print its trace. If the receiving CPU prints its trace
successfully then the sending CPU just continues, avoiding any spurious
"stale" trace.

This has the added benefit of allowing all CPUs to print their traces in
order and avoids any interleaving of their output.

Fixes: 5cc05910f26e ("powerpc/64s: Wire up arch_trigger_cpumask_backtrace()")
Cc: stable@vger.kernel.org # v4.18+
Reported-by: Nathan Lynch 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210625140408.3351173-1-mpe@ellerman.id.au
Signed-off-by: Greg Kroah-Hartman

powerpc/64s: Fix build failures with CONFIG_NMI_IPI=n

2018-06-19T13:03:50+00:00

I broke the build when CONFIG_NMI_IPI=n with my recent commit to add
arch_trigger_cpumask_backtrace(), eg:

  stacktrace.c:(.text+0x1b0): undefined reference to `.smp_send_safe_nmi_ipi'

We should rework the CONFIG symbols here in future to avoid these
double barrelled ifdefs but for now they fix the build.

Fixes: 5cc05910f26e ("powerpc/64s: Wire up arch_trigger_cpumask_backtrace()")
Reported-by: Christophe LEROY 
Signed-off-by: Michael Ellerman

powerpc/stacktrace: Update copyright

2018-06-03T10:43:43+00:00

This now has new code in it written by Nick and I, and switch to a
SPDX tag.

Signed-off-by: Michael Ellerman 
Reviewed-by: Nicholas Piggin

powerpc/64s: Wire up arch_trigger_cpumask_backtrace()

2018-06-03T10:43:43+00:00

This allows eg. the RCU stall detector, or the soft/hardlockup
detectors to trigger a backtrace on all CPUs.

We implement this by sending a "safe" NMI, which will actually only
send an IPI. Unfortunately the generic code prints "NMI", so that's a
little confusing but we can probably live with it.

If one of the CPUs doesn't respond to the IPI, we then print some info
from it's paca and do a backtrace based on its saved_r1.

Example output:

  INFO: rcu_sched detected stalls on CPUs/tasks:
  	2-...0: (0 ticks this GP) idle=1be/1/4611686018427387904 softirq=1055/1055 fqs=25735
  	(detected by 4, t=58847 jiffies, g=58, c=57, q=1258)
  Sending NMI from CPU 4 to CPUs 2:
  CPU 2 didn't respond to backtrace IPI, inspecting paca.
  irq_soft_mask: 0x01 in_mce: 0 in_nmi: 0 current: 3623 (bash)
  Back trace of paca->saved_r1 (0xc0000000e1c83ba0) (possibly stale):
  Call Trace:
  [c0000000e1c83ba0] [0000000000000014] 0x14 (unreliable)
  [c0000000e1c83bc0] [c000000000765798] lkdtm_do_action+0x48/0x80
  [c0000000e1c83bf0] [c000000000765a40] direct_entry+0x110/0x1b0
  [c0000000e1c83c90] [c00000000058e650] full_proxy_write+0x90/0xe0
  [c0000000e1c83ce0] [c0000000003aae3c] __vfs_write+0x6c/0x1f0
  [c0000000e1c83d80] [c0000000003ab214] vfs_write+0xd4/0x240
  [c0000000e1c83dd0] [c0000000003ab5cc] ksys_write+0x6c/0x110
  [c0000000e1c83e30] [c00000000000b860] system_call+0x58/0x6c

Signed-off-by: Michael Ellerman 
Reviewed-by: Nicholas Piggin

powerpc/livepatch: Fix build error with kprobes disabled.

2018-05-29T01:10:39+00:00

arch/powerpc/kernel/stacktrace.c: In function ‘save_stack_trace_tsk_reliable’:
arch/powerpc/kernel/stacktrace.c:176:28: error: ‘kretprobe_trampoline’ undeclared
   if (ip == (unsigned long)kretprobe_trampoline)
                            ^~~~~~~~~~~~~~~~~~~~

Fixes: df78d3f61480 ("powerpc/livepatch: Implement reliable stack tracing for the consistency model")
Signed-off-by: Aneesh Kumar K.V 
Signed-off-by: Michael Ellerman

powerpc/livepatch: Implement reliable stack tracing for the consistency model

2018-05-10T13:25:12+00:00

The "Power Architecture 64-Bit ELF V2 ABI" says in section 2.3.2.3:

[...] There are several rules that must be adhered to in order to ensure
reliable and consistent call chain backtracing:

* Before a function calls any other function, it shall establish its
  own stack frame, whose size shall be a multiple of 16 bytes.

 – In instances where a function’s prologue creates a stack frame, the
   back-chain word of the stack frame shall be updated atomically with
   the value of the stack pointer (r1) when a back chain is implemented.
   (This must be supported as default by all ELF V2 ABI-compliant
   environments.)
[...]
 – The function shall save the link register that contains its return
   address in the LR save doubleword of its caller’s stack frame before
   calling another function.

To me this sounds like the equivalent of HAVE_RELIABLE_STACKTRACE.
This patch may be unneccessarily limited to ppc64le, but OTOH the only
user of this flag so far is livepatching, which is only implemented on
PPCs with 64-LE, a.k.a. ELF ABI v2.

Feel free to add other ppc variants, but so far only ppc64le got tested.

This change also implements save_stack_trace_tsk_reliable() for ppc64le
that checks for the above conditions, where possible.

Signed-off-by: Torsten Duwe 
Signed-off-by: Nicolai Stange 
Acked-by: Josh Poimboeuf 
Signed-off-by: Michael Ellerman

powerpc: Make /proc/self/stack always print the current stack

2017-03-28T03:43:59+00:00

For the current task, the kernel stack would only tell the last time the
process was rescheduled, if ever. Use the current stack pointer for the
current task.

Otherwise, every once in a while, the stacktrace printed when reading
/proc/self/stack would look like the process is running in userspace,
while it's not, which some may consider as a bug.

This is also consistent with some other architectures, like x86 and arm,
at least.

Signed-off-by: Thadeu Lima de Souza Cascardo 
Signed-off-by: Michael Ellerman

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:34+00:00

We are going to split  out of , which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder  file that just
maps to  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 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

powerpc: Implement save_stack_trace_regs() to enable kprobe stack tracing

2016-01-11T03:27:28+00:00

It has come to my attention that kprobe event stack tracing does not
work on powerpc. You can see with the following:

  # cd /sys/kernel/debug/tracing
  # echo stacktrace > trace_options
  # echo 'p kfree' > kprobe_events
  # echo 1 > events/kprobes/enable

Will print the following warning:
  save_stack_trace_regs() not implemented yet.

Although save_stack_trace() (which normal event stack traces use) is
implemented, save_stack_trace_regs() which kprobe events use is not.
This is a cheap attempt to implement that function.

Note, This may have issues if a task tries to get a stack trace from
another task with its regs, because it just passes in "current" to
save_context_stack(). But this does solve the issue with stack tracing
kprobe events.

Reported-by: Chunyu Hu 
Signed-off-by: Steven Rostedt 
Signed-off-by: Michael Ellerman