Merge tag 'probes-fixes-v6.7-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull probes fixes from Masami Hiramatsu:

 - objpool: Fix objpool overrun case on memory/cache access delay
   especially on the big.LITTLE SoC. The objpool uses a copy of object
   slot index internal loop, but the slot index can be changed on
   another processor in parallel. In that case, the difference of 'head'
   local copy and the 'slot->last' index will be bigger than local slot
   size. In that case, we need to re-read the slot::head to update it.

 - kretprobe: Fix to use appropriate rcu API for kretprobe holder. Since
   kretprobe_holder::rp is RCU managed, it should use
   rcu_assign_pointer() and rcu_dereference_check() correctly. Also
   adding __rcu tag for finding wrong usage by sparse.

 - rethook: Fix to use appropriate rcu API for rethook::handler. The
   same as kretprobe, rethook::handler is RCU managed and it should use
   rcu_assign_pointer() and rcu_dereference_check(). This also adds
   __rcu tag for finding wrong usage by sparse.

* tag 'probes-fixes-v6.7-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  rethook: Use __rcu pointer for rethook::handler
  kprobes: consistent rcu api usage for kretprobe holder
  lib: objpool: fix head overrun on RK3588 SBC

1 files changed, 17 insertions, 0 deletions

diff --git a/lib/objpool.c b/lib/objpool.c
index ce0087f64400..cfdc02420884 100644
--- a/lib/objpool.c
+++ b/lib/objpool.c
@@ -201,6 +201,23 @@ static inline void *objpool_try_get_slot(struct objpool_head *pool, int cpu)
 	while (head != READ_ONCE(slot->last)) {
 		void *obj;
 
+		/*
+		 * data visibility of 'last' and 'head' could be out of
+		 * order since memory updating of 'last' and 'head' are
+		 * performed in push() and pop() independently
+		 *
+		 * before any retrieving attempts, pop() must guarantee
+		 * 'last' is behind 'head', that is to say, there must
+		 * be available objects in slot, which could be ensured
+		 * by condition 'last != head && last - head <= nr_objs'
+		 * that is equivalent to 'last - head - 1 < nr_objs' as
+		 * 'last' and 'head' are both unsigned int32
+		 */
+		if (READ_ONCE(slot->last) - head - 1 >= pool->nr_objs) {
+			head = READ_ONCE(slot->head);
+			continue;
+		}
+
 		/* obj must be retrieved before moving forward head */
 		obj = READ_ONCE(slot->entries[head & slot->mask]);