x86/dumpstack: Handle NULL stack pointer in show_trace_log_lvl()

When show_trace_log_lvl() is called from show_regs(), it completely
fails to dump the stack.  This bug was introduced when
show_stack_log_lvl() was removed with the following commit:

  0ee1dd9f5e7e ("x86/dumpstack: Remove raw stack dump")

Previous callers of that function now call show_trace_log_lvl()
directly.  That resulted in a subtle change, in that the 'stack'
argument can now be NULL in certain cases.

A NULL 'stack' pointer means that the stack dump should start from the
topmost stack frame unless 'regs' is valid, in which case it should
start from 'regs->sp'.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 0ee1dd9f5e7e ("x86/dumpstack: Remove raw stack dump")
Link: http://lkml.kernel.org/r/c551842302a9c222d96a14e42e4003f059509f69.1479362652.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 499aa6f0fde53cd6551ab0380d5459fc849c403f..1e057b01b6484612eb44f719e8b9a30aae0ab12f 100644 (file)
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -59,6 +59,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
        printk("%sCall Trace:\n", log_lvl);
 
        unwind_start(&state, task, regs, stack);
+       stack = stack ? : get_stack_pointer(task, regs);
 
        /*
         * Iterate through the stacks, starting with the current stack pointer.