arm64: make irq_stack_ptr more robust

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>

2 files changed, 16 insertions, 8 deletions

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 12a18cbc4295..d9751a4769e7 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 cbedd724f48e..c5392081b49b 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)