powerpc: Fix smp_processor_id() in preemptible splat in set_breakpoint

Currently, on 8641D, which doesn't set CONFIG_HAVE_HW_BREAKPOINT
we get the following splat:

BUG: using smp_processor_id() in preemptible [00000000] code: login/1382
caller is set_breakpoint+0x1c/0xa0
CPU: 0 PID: 1382 Comm: login Not tainted 3.15.0-rc3-00041-g2aafe1a4d451 #1
Call Trace:
[decd5d80] [c0008dc4] show_stack+0x50/0x158 (unreliable)
[decd5dc0] [c03c6fa0] dump_stack+0x7c/0xdc
[decd5de0] [c01f8818] check_preemption_disabled+0xf4/0x104
[decd5e00] [c00086b8] set_breakpoint+0x1c/0xa0
[decd5e10] [c00d4530] flush_old_exec+0x2bc/0x588
[decd5e40] [c011c468] load_elf_binary+0x2ac/0x1164
[decd5ec0] [c00d35f8] search_binary_handler+0xc4/0x1f8
[decd5ef0] [c00d4ee8] do_execve+0x3d8/0x4b8
[decd5f40] [c001185c] ret_from_syscall+0x0/0x38
 --- Exception: c01 at 0xfeee554
    LR = 0xfeee7d4

The call path in this case is:

	flush_thread
	   --> set_debug_reg_defaults
	     --> set_breakpoint
	       --> __get_cpu_var

Since preemption is enabled in the cleanup of flush thread, and
there is no need to disable it, introduce the distinction between
set_breakpoint and __set_breakpoint, leaving only the flush_thread
instance as the current user of set_breakpoint.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index b0a1792279bb..0bb5918faaaf 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -72,7 +72,7 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
          * If so, DABR will be populated in single_step_dabr_instruction().
          */
         if (current->thread.last_hit_ubp != bp)
-                set_breakpoint(info);
+                __set_breakpoint(info);
 
         return 0;
 }
@@ -198,7 +198,7 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 
         info = counter_arch_bp(tsk->thread.last_hit_ubp);
         regs->msr &= ~MSR_SE;
-        set_breakpoint(info);
+        __set_breakpoint(info);
         tsk->thread.last_hit_ubp = NULL;
 }
 
@@ -284,7 +284,7 @@ int __kprobes hw_breakpoint_handler(struct die_args *args)
         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
                 perf_bp_event(bp, regs);
 
-        set_breakpoint(info);
+        __set_breakpoint(info);
 out:
         rcu_read_unlock();
         return rc;
@@ -316,7 +316,7 @@ int __kprobes single_step_dabr_instruction(struct die_args *args)
         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
                 perf_bp_event(bp, regs);
 
-        set_breakpoint(info);
+        __set_breakpoint(info);
         current->thread.last_hit_ubp = NULL;
 
         /*