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

[PATCH 1/2] 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 (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 <christophe.leroy@c-s.fr>
---
 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

[PATCH 2/2] powerpc/kprobes: Reduce depth of a test

[Christophe Leroy]

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

Is equivalent to

	if (a & b)
		do_something();

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 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

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

[Naveen N. Rao]

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 <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/kernel/kprobes.c | 15 +--------------
>  1 file changed, 1 insertion(+), 14 deletions(-)

Good cleanup, thanks.

> 
> 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.

- Naveen

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

Re: [PATCH 2/2] powerpc/kprobes: Reduce depth of a test

[Naveen N. Rao]

Christophe Leroy wrote:
> 	if (a) {
> 		if (b)
> 			do_something();
> 	}
> 
> Is equivalent to
> 
> 	if (a & b)
> 		do_something();
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  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 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

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

[Christophe Leroy]

Le 18/02/2020 à 15:39, Naveen N. Rao a écrit :
> 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 <christophe.leroy@c-s.fr>
>> ---
>>  arch/powerpc/kernel/kprobes.c | 15 +--------------
>>  1 file changed, 1 insertion(+), 14 deletions(-)
> 
> Good cleanup, thanks.
> 
>>
>> 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