diff options
Diffstat (limited to 'fs/userfaultfd.c')
| -rw-r--r-- | fs/userfaultfd.c | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 5419e7da82ba..ef4b48d1ea42 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -381,8 +381,26 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason) * in __get_user_pages if userfaultfd_release waits on the * caller of handle_userfault to release the mmap_sem. */ - if (unlikely(ACCESS_ONCE(ctx->released))) + if (unlikely(ACCESS_ONCE(ctx->released))) { + /* + * Don't return VM_FAULT_SIGBUS in this case, so a non + * cooperative manager can close the uffd after the + * last UFFDIO_COPY, without risking to trigger an + * involuntary SIGBUS if the process was starting the + * userfaultfd while the userfaultfd was still armed + * (but after the last UFFDIO_COPY). If the uffd + * wasn't already closed when the userfault reached + * this point, that would normally be solved by + * userfaultfd_must_wait returning 'false'. + * + * If we were to return VM_FAULT_SIGBUS here, the non + * cooperative manager would be instead forced to + * always call UFFDIO_UNREGISTER before it can safely + * close the uffd. + */ + ret = VM_FAULT_NOPAGE; goto out; + } /* * Check that we can return VM_FAULT_RETRY. |