We assume to have only one reference counter for one uprobe. Don't
allow user to register multiple uprobes having same inode+offset
but different reference counter.
Though, existing tools which already support SDT events creates
normal uprobe and updates reference counter on their own. Allow 0 as
a special value for reference counter offset. I.e. two uprobes, one
having ref_ctr_offset=0 and the other having non-zero ref_ctr_offset
can coexists. This gives user a flexibility to either depend on
kernel uprobe infrastructure to maintain reference counter or just
use normal uprobe and maintain reference counter on his own.
Signed-off-by: Ravi Bangoria <ravi.bango...@linux.ibm.com>
---
kernel/events/uprobes.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 50 insertions(+), 2 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 84da8512a974..563cc3e625b3 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -63,6 +63,8 @@ static struct percpu_rw_semaphore dup_mmap_sem;
/* Have a copy of original instruction */
#define UPROBE_COPY_INSN 0
+/* Reference counter offset is reloaded with non-zero value. */
+#define REF_CTR_OFF_RELOADED 1
struct uprobe {
struct rb_node rb_node; /* node in the rb tree */
@@ -476,9 +478,23 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe,
struct mm_struct *mm,
return ret;
ret = verify_opcode(old_page, vaddr, &opcode);
- if (ret <= 0)
+ if (ret < 0)
goto put_old;
+ /*
+ * If instruction is already patched but reference counter offset
+ * has been reloaded to non-zero value, increment the reference
+ * counter and return.
+ */
+ if (ret == 0) {
+ if (is_register &&
+ test_bit(REF_CTR_OFF_RELOADED, &uprobe->flags)) {
+ WARN_ON(!uprobe->ref_ctr_offset);
+ ret = update_ref_ctr(uprobe, mm, true);
+ }
+ 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);
@@ -679,6 +695,30 @@ static struct uprobe *alloc_uprobe(struct inode *inode,
loff_t offset,
cur_uprobe = insert_uprobe(uprobe);
/* a uprobe exists for this inode:offset combination */
if (cur_uprobe) {
+ /*
+ * If inode+offset matches, ref_ctr_offset must match as
+ * well. Though, 0 is a special value for ref_ctr_offset.
+ */
+ if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset &&
+ cur_uprobe->ref_ctr_offset != 0 &&
+ uprobe->ref_ctr_offset != 0) {
+ pr_warn("Err: Reference counter mismatch.\n");
+ put_uprobe(cur_uprobe);
+ kfree(uprobe);
+ return ERR_PTR(-EINVAL);
+ }
+
+ /*
+ * If existing uprobe->ref_ctr_offset is 0 and user is
+ * registering same uprobe with non-zero ref_ctr_offset,
+ * set new ref_ctr_offset to existing uprobe.
+ */
+
+ if (!cur_uprobe->ref_ctr_offset && uprobe->ref_ctr_offset) {
+ cur_uprobe->ref_ctr_offset = uprobe->ref_ctr_offset;
+ set_bit(REF_CTR_OFF_RELOADED, &cur_uprobe->flags);
+ }
+
kfree(uprobe);
uprobe = cur_uprobe;
}
@@ -971,6 +1011,7 @@ register_for_each_vma(struct uprobe *uprobe, struct
uprobe_consumer *new)
bool is_register = !!new;
struct map_info *info;
int err = 0;
+ bool installed = false;
percpu_down_write(&dup_mmap_sem);
info = build_map_info(uprobe->inode->i_mapping,
@@ -1000,8 +1041,10 @@ register_for_each_vma(struct uprobe *uprobe, struct
uprobe_consumer *new)
if (is_register) {
/* consult only the "caller", new consumer. */
if (consumer_filter(new,
- UPROBE_FILTER_REGISTER, mm))
+ UPROBE_FILTER_REGISTER, mm)) {
err = install_breakpoint(uprobe, mm, vma,
info->vaddr);
+ installed = true;
+ }
} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
if (!filter_chain(uprobe,
UPROBE_FILTER_UNREGISTER, mm))
@@ -1016,6 +1059,8 @@ register_for_each_vma(struct uprobe *uprobe, struct
uprobe_consumer *new)
}
out:
percpu_up_write(&dup_mmap_sem);
+ if (installed)
+ clear_bit(REF_CTR_OFF_RELOADED, &uprobe->flags);
return err;
}
@@ -1093,6 +1138,9 @@ static int __uprobe_register(struct inode *inode, loff_t
offset,
uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
if (!uprobe)
return -ENOMEM;
+ if (IS_ERR(uprobe))
+ return PTR_ERR(uprobe);
+
/*
* We can race with uprobe_unregister()->delete_uprobe().
* Check uprobe_is_active() and retry if it is false.
--
2.14.4
