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>

1 files changed, 10 insertions, 1 deletions

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)