[PATCH v2] powerpc/kprobes: Remove redundant code

[PATCH v2] powerpc/kprobes: Remove redundant code

[Christophe Leroy]

At the time being we have something like

	if (something) {
		p = get();
		if (p) {
			if (something_wrong)
				goto out;
			...
			return;
		} else if (a != b) {
			if (some_error)
				goto out;
			...
		}
		goto out;
	}
	p = get();
	if (!p) {
		if (a != b) {
			if (some_error)
				goto out;
			...
		}
		goto out;
	}

This is similar to

	p = get();
	if (!p) {
		if (a != b) {
			if (some_error)
				goto out;
			...
		}
		goto out;
	}
	if (something) {
		if (something_wrong)
			goto out;
		...
		return;
	}

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
v2: Reverse the logic by testing (!p) before kprobe_running() as suggested by Naveen.
---
 arch/powerpc/kernel/kprobes.c | 80 ++++++++++++++---------------------
 1 file changed, 32 insertions(+), 48 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 9b340af02c38..84567406b53d 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -274,54 +274,6 @@ int kprobe_handler(struct pt_regs *regs)
 	preempt_disable();
 	kcb = get_kprobe_ctlblk();
 
-	/* Check we're not actually recursing */
-	if (kprobe_running()) {
-		p = get_kprobe(addr);
-		if (p) {
-			kprobe_opcode_t insn = *p->ainsn.insn;
-			if (kcb->kprobe_status == KPROBE_HIT_SS &&
-					is_trap(insn)) {
-				/* Turn off 'trace' bits */
-				regs->msr &= ~MSR_SINGLESTEP;
-				regs->msr |= kcb->kprobe_saved_msr;
-				goto no_kprobe;
-			}
-			/* We have reentered the kprobe_handler(), since
-			 * another probe was hit while within the handler.
-			 * We here save the original kprobes variables and
-			 * just single step on the instruction of the new probe
-			 * without calling any user handlers.
-			 */
-			save_previous_kprobe(kcb);
-			set_current_kprobe(p, regs, kcb);
-			kprobes_inc_nmissed_count(p);
-			kcb->kprobe_status = KPROBE_REENTER;
-			if (p->ainsn.boostable >= 0) {
-				ret = try_to_emulate(p, regs);
-
-				if (ret > 0) {
-					restore_previous_kprobe(kcb);
-					preempt_enable_no_resched();
-					return 1;
-				}
-			}
-			prepare_singlestep(p, regs);
-			return 1;
-		} else if (*addr != BREAKPOINT_INSTRUCTION) {
-			/* If trap variant, then it belongs not to us */
-			kprobe_opcode_t cur_insn = *addr;
-
-			if (is_trap(cur_insn))
-				goto no_kprobe;
-			/* The breakpoint instruction was removed by
-			 * another cpu right after we hit, no further
-			 * handling of this interrupt is appropriate
-			 */
-			ret = 1;
-		}
-		goto no_kprobe;
-	}
-
 	p = get_kprobe(addr);
 	if (!p) {
 		if (*addr != BREAKPOINT_INSTRUCTION) {
@@ -346,6 +298,38 @@ int kprobe_handler(struct pt_regs *regs)
 		goto no_kprobe;
 	}
 
+	/* Check we're not actually recursing */
+	if (kprobe_running()) {
+		kprobe_opcode_t insn = *p->ainsn.insn;
+		if (kcb->kprobe_status == KPROBE_HIT_SS && is_trap(insn)) {
+			/* Turn off 'trace' bits */
+			regs->msr &= ~MSR_SINGLESTEP;
+			regs->msr |= kcb->kprobe_saved_msr;
+			goto no_kprobe;
+		}
+		/* We have reentered the kprobe_handler(), since
+		 * another probe was hit while within the handler.
+		 * We here save the original kprobes variables and
+		 * just single step on the instruction of the new probe
+		 * without calling any user handlers.
+		 */
+		save_previous_kprobe(kcb);
+		set_current_kprobe(p, regs, kcb);
+		kprobes_inc_nmissed_count(p);
+		kcb->kprobe_status = KPROBE_REENTER;
+		if (p->ainsn.boostable >= 0) {
+			ret = try_to_emulate(p, regs);
+
+			if (ret > 0) {
+				restore_previous_kprobe(kcb);
+				preempt_enable_no_resched();
+				return 1;
+			}
+		}
+		prepare_singlestep(p, regs);
+		return 1;
+	}
+
 	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 	set_current_kprobe(p, regs, kcb);
 	if (p->pre_handler && p->pre_handler(p, regs)) {
-- 
2.25.0

Re: [PATCH v2] powerpc/kprobes: Remove redundant code

[Michael Ellerman]

On Wed, 2020-02-19 at 08:05:57 UTC, Christophe Leroy wrote:
> At the time being we have something like
> 
> 	if (something) {
> 		p = get();
> 		if (p) {
> 			if (something_wrong)
> 				goto out;
> 			...
> 			return;
> 		} else if (a != b) {
> 			if (some_error)
> 				goto out;
> 			...
> 		}
> 		goto out;
> 	}
> 	p = get();
> 	if (!p) {
> 		if (a != b) {
> 			if (some_error)
> 				goto out;
> 			...
> 		}
> 		goto out;
> 	}
> 
> This is similar to
> 
> 	p = get();
> 	if (!p) {
> 		if (a != b) {
> 			if (some_error)
> 				goto out;
> 			...
> 		}
> 		goto out;
> 	}
> 	if (something) {
> 		if (something_wrong)
> 			goto out;
> 		...
> 		return;
> 	}
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/eb4f8e259acc37b91b62ca57e0d3c8960c357843

cheers