[RFC v8 PATCH 2/5] uprobes: introduce has_uprobes helper

[Yang Shi]

We need check if mm or vma has uprobes in the following patch to check
if a vma could be unmapped with holding read mmap_sem. The checks and
pre-conditions used by uprobe_munmap() look just suitable for this
purpose.

Extracting those checks into a helper function, has_uprobes().

Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
---
 include/linux/uprobes.h |  7 +++++++
 kernel/events/uprobes.c | 23 ++++++++++++++++-------
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 0a294e9..418764e 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -149,6 +149,8 @@ struct uprobes_state {
 extern bool arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
 extern void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
 					 void *src, unsigned long len);
+extern bool has_uprobes(struct vm_area_struct *vma, unsigned long start,
+			unsigned long end);
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
 };
@@ -203,5 +205,10 @@ static inline void uprobe_copy_process(struct task_struct *t, unsigned long flag
 static inline void uprobe_clear_state(struct mm_struct *mm)
 {
 }
+static inline bool has_uprobes(struct vm_area_struct *vma, unsigned long start,
+			       unsgined long end)
+{
+	return false;
+}
 #endif /* !CONFIG_UPROBES */
 #endif	/* _LINUX_UPROBES_H */
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index aed1ba5..568481c 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1114,22 +1114,31 @@ int uprobe_mmap(struct vm_area_struct *vma)
 	return !!n;
 }
 
-/*
- * Called in context of a munmap of a vma.
- */
-void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
+bool
+has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long end)
 {
 	if (no_uprobe_events() || !valid_vma(vma, false))
-		return;
+		return false;
 
 	if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
-		return;
+		return false;
 
 	if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags) ||
 	     test_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags))
-		return;
+		return false;
 
 	if (vma_has_uprobes(vma, start, end))
+		return true;
+
+	return false;
+}
+
+/*
+ * Called in context of a munmap of a vma.
+ */
+void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
+{
+	if (has_uprobes(vma, start, end))
 		set_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags);
 }
 
-- 
1.8.3.1