diff --git a/sys/kern/vfs_quota.c b/sys/kern/vfs_quota.c
--- a/sys/kern/vfs_quota.c
+++ b/sys/kern/vfs_quota.c
@@ -432,6 +432,14 @@
 	}
 }
 
+/*
+ * NOTE: quota limits enforced here are advisory under concurrency.
+ * The spinlock is released before the caller's VFS allocates blocks,
+ * so N concurrent writers may each pass the check and collectively
+ * exceed the limit by up to (N-1)*delta before vfs_stdaccount commits.
+ * Tight enforcement would require holding the lock across the
+ * allocation, which is not feasible from this call site.
+ */
 int
 vq_write_ok(struct mount *mp, uid_t uid, gid_t gid, uint64_t delta)
 {