[PATCH 1/6] uprobes: introduce find_active_uprobe()

[Oleg Nesterov <oleg@redhat.com>]

No functional changes. Move the "find uprobe" code from
handle_swbp() to the new helper, find_active_uprobe().

Note: with or without this change, the find-active-uprobe logic
is not exactly right. We can race with another thread which unmaps
the memory with the valid uprobe before we take mm->mmap_sem. We
can't find this uprobe simply because find_vma() fails. In this
case we wrongly assume that this trap was not caused by uprobe
and send the erroneous SIGTRAP.
---
 kernel/events/uprobes.c |   31 +++++++++++++++++++------------
 1 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 29e881b..3d0a4d6 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1474,21 +1474,12 @@ static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)
 	return false;
 }
 
-/*
- * Run handler and ask thread to singlestep.
- * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
- */
-static void handle_swbp(struct pt_regs *regs)
+static struct uprobe *find_active_uprobe(unsigned long bp_vaddr)
 {
+	struct mm_struct *mm = current->mm;
+	struct uprobe *uprobe = NULL;
 	struct vm_area_struct *vma;
-	struct uprobe_task *utask;
-	struct uprobe *uprobe;
-	struct mm_struct *mm;
-	unsigned long bp_vaddr;
 
-	uprobe = NULL;
-	bp_vaddr = uprobe_get_swbp_addr(regs);
-	mm = current->mm;
 	down_read(&mm->mmap_sem);
 	vma = find_vma(mm, bp_vaddr);
 
@@ -1506,6 +1497,22 @@ static void handle_swbp(struct pt_regs *regs)
 	current->uprobe_srcu_id = -1;
 	up_read(&mm->mmap_sem);
 
+	return uprobe;
+}
+
+/*
+ * Run handler and ask thread to singlestep.
+ * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
+ */
+static void handle_swbp(struct pt_regs *regs)
+{
+	struct uprobe_task *utask;
+	struct uprobe *uprobe;
+	unsigned long bp_vaddr;
+
+	bp_vaddr = uprobe_get_swbp_addr(regs);
+	uprobe = find_active_uprobe(bp_vaddr);
+
 	if (!uprobe) {
 		/* No matching uprobe; signal SIGTRAP. */
 		send_sig(SIGTRAP, current, 0);
-- 
1.5.5.1


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