uprobes: remove is_swbp_at_addr() from register/unregister

index 78364a2..04f3259 100644
@@ -321,17 +321,6 @@ out:
  */
 int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
 {
-	int result;
-	/*
-	 * See the comment near uprobes_hash().
-	 */
-	result = is_swbp_at_addr(mm, vaddr);
-	if (result == 1)
-		return 0;
-
-	if (result)
-		return result;
-
 	return write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
 }
 

index 04f3259..100a920 100644
@@ -183,19 +183,25 @@ bool __weak is_swbp_insn(uprobe_opcode_t *insn)
 	return *insn == UPROBE_SWBP_INSN;
 }
 
+static void copy_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *opcode)
+{
+	void *kaddr = kmap_atomic(page);
+	memcpy(opcode, kaddr + (vaddr & ~PAGE_MASK), UPROBE_SWBP_INSN_SIZE);
+	kunmap_atomic(kaddr);
+}
+
 /*
  * NOTE:
  * Expect the breakpoint instruction to be the smallest size instruction for
  * the architecture. If an arch has variable length instruction and the
  * breakpoint instruction is not of the smallest length instruction
- * supported by that architecture then we need to modify read_opcode /
+ * supported by that architecture then we need to modify is_swbp_at_addr and
  * write_opcode accordingly. This would never be a problem for archs that
  * have fixed length instructions.
  */
 
 /*
  * write_opcode - write the opcode at a given virtual address.
- * @auprobe: arch breakpointing information.
  * @mm: the probed process address space.
  * @vaddr: the virtual address to store the opcode.
  * @opcode: opcode to be written at @vaddr.

@@ -206,8 +212,8 @@ bool __weak is_swbp_insn(uprobe_opcode_t *insn)
  * For mm @mm, write the opcode at @vaddr.
  * Return 0 (success) or a negative errno.
  */
-static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
-			unsigned long vaddr, uprobe_opcode_t opcode)
+static int write_opcode(struct mm_struct *mm, unsigned long vaddr,
+			uprobe_opcode_t opcode)
 {
 	struct page *old_page, *new_page;
 	void *vaddr_old, *vaddr_new;

@@ -253,40 +259,9 @@ put_old:
 	return ret;
 }
 
-/**
- * read_opcode - read the opcode at a given virtual address.
- * @mm: the probed process address space.
- * @vaddr: the virtual address to read the opcode.
- * @opcode: location to store the read opcode.
- *
- * Called with mm->mmap_sem held (for read and with a reference to
- * mm.
- *
- * For mm @mm, read the opcode at @vaddr and store it in @opcode.
- * Return 0 (success) or a negative errno.
- */
-static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t *opcode)
-{
-	struct page *page;
-	void *vaddr_new;
-	int ret;
-
-	ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
-	if (ret <= 0)
-		return ret;
-
-	vaddr_new = kmap_atomic(page);
-	vaddr &= ~PAGE_MASK;
-	memcpy(opcode, vaddr_new + vaddr, UPROBE_SWBP_INSN_SIZE);
-	kunmap_atomic(vaddr_new);
-
-	put_page(page);
-
-	return 0;
-}
-
 static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
 {
+	struct page *page;
 	uprobe_opcode_t opcode;
 	int result;
 

@@ -300,14 +275,14 @@ static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
 			goto out;
 	}
 
-	result = read_opcode(mm, vaddr, &opcode);
-	if (result)
+	result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
+	if (result < 0)
 		return result;
-out:
-	if (is_swbp_insn(&opcode))
-		return 1;
 
-	return 0;
+	copy_opcode(page, vaddr, &opcode);
+	put_page(page);
+ out:
+	return is_swbp_insn(&opcode);
 }
 
 /**

@@ -321,7 +296,7 @@ out:
  */
 int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
 {
-	return write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
+	return write_opcode(mm, vaddr, UPROBE_SWBP_INSN);
 }
 
 /**

@@ -345,7 +320,7 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
 	if (result != 1)
 		return result;
 
-	return write_opcode(auprobe, mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
+	return write_opcode(mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
 }
 
 static int match_uprobe(struct uprobe *l, struct uprobe *r)

index 17454fb..a741ba7 100644
@@ -282,32 +282,6 @@ put_old:
 	return ret;
 }
 
-static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
-{
-	struct page *page;
-	uprobe_opcode_t opcode;
-	int result;
-
-	if (current->mm == mm) {
-		pagefault_disable();
-		result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
-								sizeof(opcode));
-		pagefault_enable();
-
-		if (likely(result == 0))
-			goto out;
-	}
-
-	result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
-	if (result < 0)
-		return result;
-
-	copy_opcode(page, vaddr, &opcode);
-	put_page(page);
- out:
-	return is_swbp_insn(&opcode);
-}
-
 /**
  * set_swbp - store breakpoint at a given address.
  * @auprobe: arch specific probepoint information.

@@ -589,29 +563,6 @@ static int copy_insn(struct uprobe *uprobe, struct file *filp)
 	return __copy_insn(mapping, filp, uprobe->arch.insn, bytes, uprobe->offset);
 }
 
-/*
- * How mm->uprobes_state.count gets updated
- * uprobe_mmap() increments the count if
- * 	- it successfully adds a breakpoint.
- * 	- it cannot add a breakpoint, but sees that there is a underlying
- * 	  breakpoint (via a is_swbp_at_addr()).
- *
- * uprobe_munmap() decrements the count if
- * 	- it sees a underlying breakpoint, (via is_swbp_at_addr)
- * 	  (Subsequent uprobe_unregister wouldnt find the breakpoint
- * 	  unless a uprobe_mmap kicks in, since the old vma would be
- * 	  dropped just after uprobe_munmap.)
- *
- * uprobe_register increments the count if:
- * 	- it successfully adds a breakpoint.
- *
- * uprobe_unregister decrements the count if:
- * 	- it sees a underlying breakpoint and removes successfully.
- * 	  (via is_swbp_at_addr)
- * 	  (Subsequent uprobe_munmap wouldnt find the breakpoint
- * 	  since there is no underlying breakpoint after the
- * 	  breakpoint removal.)
- */
 static int
 install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
 			struct vm_area_struct *vma, unsigned long vaddr)

@@ -1389,6 +1340,30 @@ static void mmf_recalc_uprobes(struct mm_struct *mm)
 	clear_bit(MMF_HAS_UPROBES, &mm->flags);
 }
 
+static int is_swbp_at_addr(struct mm_struct *mm, unsigned long vaddr)
+{
+	struct page *page;
+	uprobe_opcode_t opcode;
+	int result;
+
+	pagefault_disable();
+	result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
+							sizeof(opcode));
+	pagefault_enable();
+
+	if (likely(result == 0))
+		goto out;
+
+	result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
+	if (result < 0)
+		return result;
+
+	copy_opcode(page, vaddr, &opcode);
+	put_page(page);
+ out:
+	return is_swbp_insn(&opcode);
+}
+
 static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
 {
 	struct mm_struct *mm = current->mm;

index 100a920..17454fb 100644
@@ -190,6 +190,25 @@ static void copy_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t
 	kunmap_atomic(kaddr);
 }
 
+static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
+{
+	uprobe_opcode_t old_opcode;
+	bool is_swbp;
+
+	copy_opcode(page, vaddr, &old_opcode);
+	is_swbp = is_swbp_insn(&old_opcode);
+
+	if (is_swbp_insn(new_opcode)) {
+		if (is_swbp)		/* register: already installed? */
+			return 0;
+	} else {
+		if (!is_swbp)		/* unregister: was it changed by us? */
+			return -EINVAL;
+	}
+
+	return 1;
+}
+
 /*
  * NOTE:
  * Expect the breakpoint instruction to be the smallest size instruction for

@@ -226,6 +245,10 @@ retry:
 	if (ret <= 0)
 		return ret;
 
+	ret = verify_opcode(old_page, vaddr, &opcode);
+	if (ret <= 0)
+		goto put_old;
+
 	ret = -ENOMEM;
 	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
 	if (!new_page)

@@ -311,15 +334,6 @@ int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned
 int __weak
 set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
 {
-	int result;
-
-	result = is_swbp_at_addr(mm, vaddr);
-	if (!result)
-		return -EINVAL;
-
-	if (result != 1)
-		return result;
-
 	return write_opcode(mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
 }
 

@@ -178,6 +178,11 @@ static int __replace_page(struct vm_area
  * Default implementation of is_swbp_insn
  * Returns true if @insn is a breakpoint instruction.
  */
+static bool is_uprobe_opcode(uprobe_opcode_t *insn)
+{
+	return *insn == UPROBE_SWBP_INSN;
+}
+
 bool __weak is_swbp_insn(uprobe_opcode_t *insn)
 {
 	return *insn == UPROBE_SWBP_INSN;

@@ -196,9 +201,9 @@ static int verify_opcode(struct page *pa
 	bool is_swbp;
 
 	copy_opcode(page, vaddr, &old_opcode);
-	is_swbp = is_swbp_insn(&old_opcode);
+	is_swbp = is_uprobe_opcode(&old_opcode);
 
-	if (is_swbp_insn(new_opcode)) {
+	if (is_uprobe_opcode(new_opcode)) {
 		if (is_swbp)		/* register: already installed? */
 			return 0;
 	} else {

@@ -585,7 +590,7 @@ install_breakpoint(struct uprobe *uprobe
 		if (ret)
 			return ret;
 
-		if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
+		if (is_uprobe_opcode((uprobe_opcode_t *)uprobe->arch.insn))
 			return -ENOTSUPP;
 
 		ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, vaddr);