[tip:x86/asm] x86/dumpstack: Handle NULL stack pointer in show_trace_log_lvl()

[tip-bot for Josh Poimboeuf]

Commit-ID:  f4474c9f0bba17857b1a47c8dc89c07a0845c2b2
Gitweb:     http://git.kernel.org/tip/f4474c9f0bba17857b1a47c8dc89c07a0845c2b2
Author:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Thu, 17 Nov 2016 00:04:58 -0600
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 17 Nov 2016 07:48:39 +0100

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@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 0ee1dd9f5e7e ("x86/dumpstack: Remove raw stack dump")
Link: http://lkml.kernel.org/r/c551842302a9c222d96a14e42e4003f059509f69.1479362652.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/dumpstack.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 499aa6f..1e057b0 100644
--- 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.