[dpdk-stable] [PATCH] malloc: don't skip pad on free

[Anatoly Burakov]

Previously, we were skipping erasing pad because we were
expecting it to be freed when we were merging adjacent
segments. However, if there were no adjacent segments to
merge, we would've skipped erasing the pad, leaving non-zero
memory in our free space.

Fix this by including pad in the erasing unconditionally.

Fixes: e43a9f52b7ff ("malloc: fix pad erasing")
Cc: stable at dpdk.org

Reported-by: Andrew Rybchenko <arybchenko at solarflare.com>

Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
---

Notes:
    I have confirmed the issue with unit tests - adding a simple zero-check
    function on alloc will throw errors when running malloc_autotest on
    latest master, but the errors go away once this patch is applied.
    
    Our unit test's zmalloc calls check if memory is not zero, but this
    condition is rare enough not to be triggered by it, and regular
    malloc calls aren't checked on zeroed out memory. The bulk of the
    malloc calls in the unit tests are malloc, not zmalloc, so pretty
    much all of the time the memory is not checked for being zero on
    alloc.

 lib/librte_eal/common/malloc_elem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/librte_eal/common/malloc_elem.c b/lib/librte_eal/common/malloc_elem.c
index efcb82677..e0a8ed15b 100644
--- a/lib/librte_eal/common/malloc_elem.c
+++ b/lib/librte_eal/common/malloc_elem.c
@@ -519,8 +519,8 @@ malloc_elem_free(struct malloc_elem *elem)
 	void *ptr;
 	size_t data_len;
 
-	ptr = RTE_PTR_ADD(elem, MALLOC_ELEM_HEADER_LEN + elem->pad);
-	data_len = elem->size - elem->pad - MALLOC_ELEM_OVERHEAD;
+	ptr = RTE_PTR_ADD(elem, MALLOC_ELEM_HEADER_LEN);
+	data_len = elem->size - MALLOC_ELEM_OVERHEAD;
 
 	elem = malloc_elem_join_adjacent_free(elem);
 
-- 
2.17.1