[PATCH] i386: break out of recursion in stackframe walk

If CONFIG_FRAME_POINTERS is enabled, and one does a dump_stack() during
early SMP init, an infinite stackdump and a bootup hang happens:

 [<c0104e7f>] show_trace+0xd/0xf
 [<c0104e96>] dump_stack+0x15/0x17
 [<c01440df>] save_trace+0xc3/0xce
 [<c014527d>] mark_lock+0x8c/0x4fe
 [<c0145df5>] __lockdep_acquire+0x44e/0xaa5
 [<c0146798>] lockdep_acquire+0x68/0x84
 [<c1048699>] _spin_lock+0x21/0x2f
 [<c010d918>] prepare_set+0xd/0x5d
 [<c010daa8>] generic_set_all+0x1d/0x201
 [<c010ca9a>] mtrr_ap_init+0x23/0x3b
 [<c010ada8>] identify_cpu+0x2a7/0x2af
 [<c01192a7>] smp_store_cpu_info+0x2f/0xb4
 [<c01197d0>] start_secondary+0xb5/0x3ec
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [<c104ec11>] end_of_stack_stop_unwind_function+0x1/0x4
 [...]

Due to "end_of_stack_stop_unwind_function" recursing back to itself in the
EBP stackframe-walker.  So avoid this type of recursion when walking the
stack .

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/traps.c

@@ -149,6 +149,12 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo,
 	while (valid_stack_ptr(tinfo, (void *)ebp)) {
 		addr = *(unsigned long *)(ebp + 4);
 		printed = print_addr_and_symbol(addr, log_lvl, printed);
+		/*
+		 * break out of recursive entries (such as
+		 * end_of_stack_stop_unwind_function):
+	 	 */
+		if (ebp == *(unsigned long *)ebp)
+			break;
 		ebp = *(unsigned long *)ebp;
 	}
 #else