diff options
Diffstat (limited to 'mm/mremap.c')
| -rw-r--r-- | mm/mremap.c | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/mm/mremap.c b/mm/mremap.c index a9617e72e6b7..7f9f9180e401 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -521,6 +521,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, unsigned long ret = -EINVAL; unsigned long charged = 0; bool locked = false; + bool downgraded = false; struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX; LIST_HEAD(uf_unmap_early); LIST_HEAD(uf_unmap); @@ -557,12 +558,20 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, /* * Always allow a shrinking remap: that just unmaps * the unnecessary pages.. - * do_munmap does all the needed commit accounting + * __do_munmap does all the needed commit accounting, and + * downgrades mmap_sem to read if so directed. */ if (old_len >= new_len) { - ret = do_munmap(mm, addr+new_len, old_len - new_len, &uf_unmap); - if (ret && old_len != new_len) + int retval; + + retval = __do_munmap(mm, addr+new_len, old_len - new_len, + &uf_unmap, true); + if (retval < 0 && old_len != new_len) { + ret = retval; goto out; + /* Returning 1 indicates mmap_sem is downgraded to read. */ + } else if (retval == 1) + downgraded = true; ret = addr; goto out; } @@ -627,7 +636,10 @@ out: vm_unacct_memory(charged); locked = 0; } - up_write(¤t->mm->mmap_sem); + if (downgraded) + up_read(¤t->mm->mmap_sem); + else + up_write(¤t->mm->mmap_sem); if (locked && new_len > old_len) mm_populate(new_addr + old_len, new_len - old_len); userfaultfd_unmap_complete(mm, &uf_unmap_early); |