[PATCH 1/2] powerpc/kprobes: Remove redundant code

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

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/kernel/kprobes.c | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index f8b848aa65bd..7a925eb76ec0 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c

@@ -276,8 +276,8 @@ int kprobe_handler(struct pt_regs *regs)
 	kcb = get_kprobe_ctlblk();
 
 	/* Check we're not actually recursing */
+	p = get_kprobe(addr);
 	if (kprobe_running()) {
-		p = get_kprobe(addr);
 		if (p) {
 			kprobe_opcode_t insn = *p->ainsn.insn;
 			if (kcb->kprobe_status == KPROBE_HIT_SS &&

@@ -308,22 +308,9 @@ int kprobe_handler(struct pt_regs *regs)
 			}
 			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) {
 			/*

-- 
2.25.0

	if (a) {
		if (b)
			do_something();
	}

Is equivalent to

	if (a & b)
		do_something();

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/kernel/kprobes.c | 58 +++++++++++++++++------------------
 1 file changed, 28 insertions(+), 30 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 7a925eb76ec0..d7c80a078c1e 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c

@@ -277,38 +277,36 @@ int kprobe_handler(struct pt_regs *regs)
 
 	/* Check we're not actually recursing */
 	p = get_kprobe(addr);
-	if (kprobe_running()) {
-		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;
-				}
+	if (kprobe_running() && 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;
 		}
+		prepare_singlestep(p, regs);
+		return 1;
 	}
 
 	if (!p) {

-- 
2.25.0

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

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/kernel/kprobes.c | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

Good cleanup, thanks.

A minot nit -- removing the above goto makes a slight change to the 
logic. But, see my comments for the next patch.

- Naveen

 	}
 
-	p = get_kprobe(addr);
 	if (!p) {
 		if (*addr != BREAKPOINT_INSTRUCTION) {
 			/*
-- 
2.25.0

Christophe Leroy wrote:

If we move the below !p case before the check for kprobe_running() right 
after get_kprobe(), we won't need to check for (p) above and we won't 
have any change in logic from Patch 1.

 	if (!p) {

- Naveen

Le 18/02/2020 à 15:39, Naveen N. Rao a écrit :

Christophe Leroy wrote:

quoted

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

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/kernel/kprobes.c | 15 +--------------
 1 file changed, 1 insertion(+), 14 deletions(-)

Good cleanup, thanks.

quoted

diff --git a/arch/powerpc/kernel/kprobes.c 

b/arch/powerpc/kernel/kprobes.c
index f8b848aa65bd..7a925eb76ec0 100644

--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c

@@ -276,8 +276,8 @@ int kprobe_handler(struct pt_regs *regs)

     kcb = get_kprobe_ctlblk();

     /* Check we're not actually recursing */
+    p = get_kprobe(addr);
     if (kprobe_running()) {
-        p = get_kprobe(addr);
         if (p) {
             kprobe_opcode_t insn = *p->ainsn.insn;
             if (kcb->kprobe_status == KPROBE_HIT_SS &&

@@ -308,22 +308,9 @@ int kprobe_handler(struct pt_regs *regs)

             }
             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;

A minot nit -- removing the above goto makes a slight change to the 
logic. But, see my comments for the next patch.

All legs of the (p) case are have either a return or a goto, so that 
goto no_kprobe is limited to the !p case, we have to fall_through now.

Christophe