uprobes: Introduce uprobe_is_active()

The lifetime of uprobe->rb_node and uprobe->inode is not refcounted,
delete_uprobe() is called when we detect that uprobe has no consumers,
and it would be deadly wrong to do this twice.

Change delete_uprobe() to WARN() if it was already called. We use
RB_CLEAR_NODE() to mark uprobe "inactive", then RB_EMPTY_NODE() can
be used to detect this case.

RB_EMPTY_NODE() is not used directly, we add the trivial helper for
the next change.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Anton Arapov <anton@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 5d38b40644b8..358baddc8ac2 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -669,6 +669,10 @@ remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vad
         return set_orig_insn(&uprobe->arch, mm, vaddr);
 }
 
+static inline bool uprobe_is_active(struct uprobe *uprobe)
+{
+        return !RB_EMPTY_NODE(&uprobe->rb_node);
+}
 /*
  * There could be threads that have already hit the breakpoint. They
  * will recheck the current insn and restart if find_uprobe() fails.
@@ -676,9 +680,13 @@ remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vad
  */
 static void delete_uprobe(struct uprobe *uprobe)
 {
+        if (WARN_ON(!uprobe_is_active(uprobe)))
+                return;
+
         spin_lock(&uprobes_treelock);
         rb_erase(&uprobe->rb_node, &uprobes_tree);
         spin_unlock(&uprobes_treelock);
+        RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */
         iput(uprobe->inode);
         put_uprobe(uprobe);
 }