powerpc: prep stack walkers for THREAD_INFO_IN_TASK

[text copied from commit 9bbd4c56b0b6
("arm64: prep stack walkers for THREAD_INFO_IN_TASK")]

When CONFIG_THREAD_INFO_IN_TASK is selected, task stacks may be freed
before a task is destroyed. To account for this, the stacks are
refcounted, and when manipulating the stack of another task, it is
necessary to get/put the stack to ensure it isn't freed and/or re-used
while we do so.

This patch reworks the powerpc stack walking code to account for this.
When CONFIG_THREAD_INFO_IN_TASK is not selected these perform no
refcounting, and this should only be a structural change that does not
affect behaviour.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Move try_get_task_stack() below tsk == NULL check in show_stack()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 71bad4b6f80dee900adfea7ba136aa46b1872c6d..791bd8ea475dee34b5f1df6e5d93b8511a0030ac 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2027,7 +2027,7 @@ int validate_sp(unsigned long sp, struct task_struct *p,
 
 EXPORT_SYMBOL(validate_sp);
 
-unsigned long get_wchan(struct task_struct *p)
+static unsigned long __get_wchan(struct task_struct *p)
 {
        unsigned long ip, sp;
        int count = 0;
@@ -2053,6 +2053,20 @@ unsigned long get_wchan(struct task_struct *p)
        return 0;
 }
 
+unsigned long get_wchan(struct task_struct *p)
+{
+       unsigned long ret;
+
+       if (!try_get_task_stack(p))
+               return 0;
+
+       ret = __get_wchan(p);
+
+       put_task_stack(p);
+
+       return ret;
+}
+
 static int kstack_depth_to_print = CONFIG_PRINT_STACK_DEPTH;
 
 void show_stack(struct task_struct *tsk, unsigned long *stack)
@@ -2067,9 +2081,13 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
        int curr_frame = 0;
 #endif
 
-       sp = (unsigned long) stack;
        if (tsk == NULL)
                tsk = current;
+
+       if (!try_get_task_stack(tsk))
+               return;
+
+       sp = (unsigned long) stack;
        if (sp == 0) {
                if (tsk == current)
                        sp = current_stack_pointer();
@@ -2081,7 +2099,7 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
        printk("Call Trace:\n");
        do {
                if (!validate_sp(sp, tsk, STACK_FRAME_OVERHEAD))
-                       return;
+                       break;
 
                stack = (unsigned long *) sp;
                newsp = stack[0];
@@ -2121,6 +2139,8 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
 
                sp = newsp;
        } while (count++ < kstack_depth_to_print);
+
+       put_task_stack(tsk);
 }
 
 #ifdef CONFIG_PPC64

diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index cf31ce6c1f53df272d44768be8de14f0733143e6..f958f3bcba0486075167bafddcd111f565aa6576 100644 (file)
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -67,12 +67,17 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
        unsigned long sp;
 
+       if (!try_get_task_stack(tsk))
+               return;
+
        if (tsk == current)
                sp = current_stack_pointer();
        else
                sp = tsk->thread.ksp;
 
        save_context_stack(trace, sp, tsk, 0);
+
+       put_task_stack(tsk);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
@@ -90,9 +95,8 @@ EXPORT_SYMBOL_GPL(save_stack_trace_regs);
  *
  * If the task is not 'current', the caller *must* ensure the task is inactive.
  */
-int
-save_stack_trace_tsk_reliable(struct task_struct *tsk,
-                               struct stack_trace *trace)
+static int __save_stack_trace_tsk_reliable(struct task_struct *tsk,
+                                          struct stack_trace *trace)
 {
        unsigned long sp;
        unsigned long newsp;
@@ -197,6 +201,25 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
        }
        return 0;
 }
+
+int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+                                 struct stack_trace *trace)
+{
+       int ret;
+
+       /*
+        * If the task doesn't have a stack (e.g., a zombie), the stack is
+        * "reliably" empty.
+        */
+       if (!try_get_task_stack(tsk))
+               return 0;
+
+       ret = __save_stack_trace_tsk_reliable(tsk, trace);
+
+       put_task_stack(tsk);
+
+       return ret;
+}
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk_reliable);
 #endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */