if (!zeropage) { /* COPY */
page_kaddr = kmap_local_folio(folio, 0);
+ /*
+ * The read mmap_lock is held here. Despite the
+ * mmap_lock being read recursive a deadlock is still
+ * possible if a writer has taken a lock. For example:
+ *
+ * process A thread 1 takes read lock on own mmap_lock
+ * process A thread 2 calls mmap, blocks taking write lock
+ * process B thread 1 takes page fault, read lock on own mmap lock
+ * process B thread 2 calls mmap, blocks taking write lock
+ * process A thread 1 blocks taking read lock on process B
+ * process B thread 1 blocks taking read lock on process A
+ *
+ * Disable page faults to prevent potential deadlock
+ * and retry the copy outside the mmap_lock.
+ */
+ pagefault_disable();
ret = copy_from_user(page_kaddr,
(const void __user *)src_addr,
PAGE_SIZE);
+ pagefault_enable();
kunmap_local(page_kaddr);
/* fallback to copy_from_user outside mmap_lock */