[PATCH RFCv3 03/23] uprobes: Move ref_ctr_offset update out of uprobe_write_opcode

Jiri Olsa
2025-03-20T11:42:40Z

The uprobe_write_opcode function currently updates also refctr offset
if there's one defined for uprobe.

This is not handy for following changes which needs to make several
updates (writes) to install or remove uprobe, but update refctr offset
just once.

Adding set_swbp_refctr/set_orig_refctr which makes sure refctr offset
is updated.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
kernel/events/uprobes.c | 50 ++++++++++++++++++++++++++---------------
1 file changed, 32 insertions(+), 18 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 5c9fc31c50f1..77b85b19f4c2 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -473,15 +473,13 @@ static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
unsigned long vaddr, uprobe_opcode_t opcode)
{
- struct uprobe *uprobe;
struct page *old_page, *new_page;
struct vm_area_struct *vma;
- int ret, is_register, ref_ctr_updated = 0;
+ int ret, is_register;
bool orig_page_huge = false;
unsigned int gup_flags = FOLL_FORCE;

is_register = is_swbp_insn(&opcode);
- uprobe = container_of(auprobe, struct uprobe, arch);

retry:
if (is_register)
@@ -506,15 +504,6 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
goto put_old;
}

- /* We are going to replace instruction, update ref_ctr. */
- if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
- ret = update_ref_ctr(uprobe, mm, is_register ? 1 : -1);
- if (ret)
- goto put_old;
-
- ref_ctr_updated = 1;
- }
-
ret = 0;
if (!is_register && !PageAnon(old_page))
goto put_old;
@@ -565,10 +554,6 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
if (unlikely(ret == -EAGAIN))
goto retry;

- /* Revert back reference counter if instruction update failed. */
- if (ret && is_register && ref_ctr_updated)
- update_ref_ctr(uprobe, mm, -1);
-
/* try collapse pmd for compound page */
if (!ret && orig_page_huge)
collapse_pte_mapped_thp(mm, vaddr, false);
@@ -590,6 +575,25 @@ int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned
return uprobe_write_opcode(auprobe, mm, vaddr, UPROBE_SWBP_INSN);
}

+static int set_swbp_refctr(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
+{
+ int err;
+
+ /* We are going to replace instruction, update ref_ctr. */
+ if (uprobe->ref_ctr_offset) {
+ err = update_ref_ctr(uprobe, mm, 1);
+ if (err)
+ return err;
+ }
+
+ err = set_swbp(&uprobe->arch, mm, vaddr);
+
+ /* Revert back reference counter if instruction update failed. */
+ if (err && uprobe->ref_ctr_offset)
+ update_ref_ctr(uprobe, mm, -1);
+ return err;
+}
+
/**
* set_orig_insn - Restore the original instruction.
* @mm: the probed process address space.
@@ -606,6 +610,16 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
*(uprobe_opcode_t *)&auprobe->insn);
}

+static int set_orig_refctr(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
+{
+ int err = set_orig_insn(&uprobe->arch, mm, vaddr);
+
+ /* Revert back reference counter even if instruction update failed. */
+ if (uprobe->ref_ctr_offset)
+ update_ref_ctr(uprobe, mm, -1);
+ return err;
+}
+
/* uprobe should have guaranteed positive refcount */
static struct uprobe *get_uprobe(struct uprobe *uprobe)
{
@@ -1142,7 +1156,7 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
if (first_uprobe)
set_bit(MMF_HAS_UPROBES, &mm->flags);

- ret = set_swbp(&uprobe->arch, mm, vaddr);
+ ret = set_swbp_refctr(uprobe, mm, vaddr);
if (!ret)
clear_bit(MMF_RECALC_UPROBES, &mm->flags);
else if (first_uprobe)
@@ -1155,7 +1169,7 @@ static int
remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
{
set_bit(MMF_RECALC_UPROBES, &mm->flags);
- return set_orig_insn(&uprobe->arch, mm, vaddr);
+ return set_orig_refctr(uprobe, mm, vaddr);
}

struct map_info {
--
2.49.0