[glibc/nsz/mtag] malloc: Avoid taggig mmaped memory on free

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=3387a579c77328cd5e793da028dd432c9a01e8b1

commit 3387a579c77328cd5e793da028dd432c9a01e8b1
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Feb 4 11:52:14 2021 +0000

    malloc: Avoid taggig mmaped memory on free
    
    Either the memory belongs to the dumped area, in which case we don't
    want to tag (the dumped area has the same tag as malloc internal data
    so tagging is unnecessary, but chunks there may not have the right
    alignment for the tag granule), or the memory will be unmapped
    immediately (and thus tagging is not useful).

Diff:
---
 malloc/malloc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 4538a01614..b4c800bd7f 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3284,9 +3284,6 @@ __libc_free (void *mem)
 
   p = mem2chunk (mem);
 
-  /* Mark the chunk as belonging to the library again.  */
-  (void)TAG_REGION (chunk2rawmem (p), CHUNK_AVAILABLE_SIZE (p) - CHUNK_HDR_SZ);
-
   if (chunk_is_mmapped (p))                       /* release mmapped memory. */
     {
       /* See if the dynamic brk/mmap threshold needs adjusting.
@@ -3307,6 +3304,10 @@ __libc_free (void *mem)
     {
       MAYBE_INIT_TCACHE ();
 
+      /* Mark the chunk as belonging to the library again.  */
+      (void)TAG_REGION (chunk2rawmem (p),
+			CHUNK_AVAILABLE_SIZE (p) - CHUNK_HDR_SZ);
+
       ar_ptr = arena_for_chunk (p);
       _int_free (ar_ptr, p, 0);
     }