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>

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 12a18cbc4295550aae7dc8a390d9b314cbcd0095..d9751a4769e758b220181d6a400bd5a238c2cedb 100644 (file)
--- 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 cbedd724f48efcf487e443fa3fc21516d8d898a6..c5392081b49ba4ac4f48d9a0782442ac888ed222 100644 (file)
--- 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)