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-rw-r--r--mm/mremap.c20
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(&current->mm->mmap_sem);
+ if (downgraded)
+ up_read(&current->mm->mmap_sem);
+ else
+ up_write(&current->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);