[PATCH] arm64: make irq_stack_ptr more robust

From: Yang Shi
Date: Thu Feb 11 2016 - 17:15:58 EST


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.

Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxx>
---
arch/arm64/kernel/stacktrace.c | 13 ++++++-------
arch/arm64/kernel/traps.c | 11 ++++++++++-
2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 12a18cb..d9751a4 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -44,14 +44,13 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
unsigned long irq_stack_ptr;

/*
- * Use raw_smp_processor_id() to avoid false-positives from
- * CONFIG_DEBUG_PREEMPT. get_wchan() calls unwind_frame() on sleeping
- * task stacks, we can be pre-empted in this case, so
- * {raw_,}smp_processor_id() may give us the wrong value. Sleeping
- * tasks can't ever be on an interrupt stack, so regardless of cpu,
- * the checks will always fail.
+ * Switching between stacks is valid when tracing current and in
+ * non-preemptible context.
*/
- irq_stack_ptr = IRQ_STACK_PTR(raw_smp_processor_id());
+ if (tsk == current && !preemptible())
+ irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
+ else
+ irq_stack_ptr = 0;

low = frame->sp;
/* irq stacks are not THREAD_SIZE aligned */
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index cbedd72..7d8db3a 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -146,9 +146,18 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
struct stackframe frame;
- unsigned long irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
+ unsigned long irq_stack_ptr;
int skip;

+ /*
+ * Switching between stacks is valid when tracing current and in
+ * non-preemptible context.
+ */
+ if (tsk == current && !preemptible())
+ irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
+ else
+ irq_stack_ptr = 0;
+
pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

if (!tsk)
--
2.0.2