uprobes/powerpc: Do not use arch_uprobe_*_step() helpers

No functional changes.

powerpc is the only user of arch_uprobe_enable/disable_step() helpers,
but they should die. They can not be used correctly, every arch needs
its own implementation (like x86 does). And they do not really help
even as initial-and-almost-working code, arch_uprobe_*_xol() hooks can
easily use user_enable/disable_single_step() directly.

Change arch_uprobe_*_step() to do nothing, and convert powerpc to use
ptrace helpers. This is equally wrong, powerpc needs the arch-specific
fixes.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

arch/powerpc/kernel/uprobes.c

@@ -64,6 +64,8 @@ int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	autask->saved_trap_nr = current->thread.trap_nr;
 	current->thread.trap_nr = UPROBE_TRAP_NR;
 	regs->nip = current->utask->xol_vaddr;
+
+	user_enable_single_step(current);
 	return 0;
 }
 
@@ -119,6 +121,8 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	 * to be executed.
 	 */
 	regs->nip = utask->vaddr + MAX_UINSN_BYTES;
+
+	user_disable_single_step(current);
 	return 0;
 }
 
@@ -162,6 +166,8 @@ void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 
 	current->thread.trap_nr = utask->autask.saved_trap_nr;
 	instruction_pointer_set(regs, utask->vaddr);
+
+	user_disable_single_step(current);
 }
 
 /*

kernel/events/uprobes.c

@@ -1432,12 +1432,10 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
 
 void __weak arch_uprobe_enable_step(struct arch_uprobe *arch)
 {
-	user_enable_single_step(current);
 }
 
 void __weak arch_uprobe_disable_step(struct arch_uprobe *arch)
 {
-	user_disable_single_step(current);
 }
 
 /*