Make io_fwrite safe for compaction

[Bug #20169]

Embedded strings are not safe for system calls without the GVL because
compaction can cause pages to be locked causing the operation to fail
with EFAULT. This commit changes io_fwrite to use rb_str_tmp_frozen_no_embed_acquire,
which guarantees that the return string is not embedded.

1 files changed, 1 insertions, 1 deletions

diff --git a/io.c b/io.c
index 7d8b9bf410..eb2698d047 100644
--- a/io.c
+++ b/io.c
@@ -1975,7 +1975,7 @@ io_fwrite(VALUE str, rb_io_t *fptr, int nosync)
     if (converted)
         OBJ_FREEZE(str);
 
-    tmp = rb_str_tmp_frozen_acquire(str);
+    tmp = rb_str_tmp_frozen_no_embed_acquire(str);
     RSTRING_GETMEM(tmp, ptr, len);
     n = io_binwrite(tmp, ptr, len, fptr, nosync);
     rb_str_tmp_frozen_release(str, tmp);