Re: [External] Re: [PATCH] eal: fix modify data area after memset

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 23 Oct 2023 17:07:21 +0800
Fengnan Chang <changfengnan@bytedance.com> wrote:

> Dmitry Kozlyuk <dmitry.kozliuk@gmail.com> 于2023年10月23日周一 04:22写道：
> >
> > 2023-09-22 16:12 (UTC+0800), Fengnan Chang:  
> > > ping
> > >
> > > Fengnan Chang <changfengnan@bytedance.com> 于2023年9月12日周二 17:05写道：  
> > > >
> > > > Let's look at this path:
> > > > malloc_elem_free  
> > > >    ->malloc_elem_join_adjacent_free
> > > >       ->join_elem(elem, elem->next)  
> > > >
> > > > 0. cur elem's pad > 0
> > > > 1. data area memset in malloc_elem_free first.
> > > > 2. next elem is free, try to join cur elem and next.
> > > > 3. in join_elem, try to modify inner->size, this address had
> > > > memset in step 1, it casue the content of addrees become non-zero.
> > > >
> > > > If user call rte_zmalloc, and pick this elem, it can't get all
> > > > zero'd memory.  
> >
> > malloc_elem_join_adjacent_free() always calls memset() after join_elem(),
> > for the next and the previous element respectively.  
> when try to call join_elem() for the next element in
> malloc_elem_join_adjacent_free(),
> the memset is try to memset *next* element, but join_elem() is update
> *current* element's
> content, which shoudn't happen, it's two different element.
> 
> > How to reproduce this bug?  
> when I test this patch,
> https://patches.dpdk.org/project/dpdk/patch/20230831111937.60975-1-changfengnan@bytedance.com/
> I have a case try to alloc 64/128/192 size object and free with 16 threads,
> after every
> alloc I'll check wheather all content is 0 or not.
> It's not easy to reproduce, you can have a try, it's easier to find
> this problem in code level.

I tried to make a test that would reproduce the problem but it did not.

diff --git a/app/test/test_malloc.c b/app/test/test_malloc.c
index cd579c503cf5..cfd45d6a28eb 100644
--- a/app/test/test_malloc.c
+++ b/app/test/test_malloc.c
@@ -28,6 +28,7 @@
 #include <rte_string_fns.h>

 #define N 10000
+#define BINS 100

 static int
 is_mem_on_socket(int32_t socket);
@@ -69,13 +70,24 @@ is_aligned(void *p, int align)
 	return 1;
 }

+static bool is_all_zero(uint8_t *mem, size_t sz)
+{
+	size_t i;
+
+	for (i = 0; i < sz; i++)
+		if (mem[i] != 0)
+			return false;
+
+	return true;
+}
+
 static int
 test_align_overlap_per_lcore(__rte_unused void *arg)
 {
 	const unsigned align1 = 8,
 			align2 = 64,
 			align3 = 2048;
-	unsigned i,j;
+	unsigned int i;
 	void *p1 = NULL, *p2 = NULL, *p3 = NULL;
 	int ret = 0;

@@ -86,11 +98,12 @@ test_align_overlap_per_lcore(__rte_unused void *arg)
 			ret = -1;
 			break;
 		}
-		for(j = 0; j < 1000 ; j++) {
-			if( *(char *)p1 != 0) {
-				printf("rte_zmalloc didn't zero the allocated memory\n");
-				ret = -1;
-			}
+
+		if (!is_all_zero(p1, 1000)) {
+			printf("rte_zmalloc didn't zero the allocated memory\n");
+			ret = -1;
+			rte_free(p1);
+			break;
 		}
 		p2 = rte_malloc("dummy", 1000, align2);
 		if (!p2){
@@ -140,6 +153,66 @@ test_align_overlap_per_lcore(__rte_unused void *arg)
 	return ret;
 }

+/*
+ * Allocate random size chunks and make sure that they are
+ * always zero.
+ */
+static int
+test_zmalloc(__rte_unused void *arg)
+{
+	unsigned int i, n;
+	void *slots[BINS] = { };
+			void *p1;
+	size_t sz;
+
+	/* Allocate many variable size chunks */
+	for (i = 0; i < BINS; i++) {
+		sz = rte_rand_max(1024) + 1;
+		p1 = rte_zmalloc("slots", sz, 0);
+		if (p1 == NULL) {
+			printf("rte_zmalloc(%zu) returned NULL (i=%u)\n", sz, i);
+			goto fail;
+		}
+		slots[i] = p1;
+		if (!is_all_zero(p1, sz))
+			goto fail;
+	}
+
+	/* Drop one chunk per iteration */
+	for (n = BINS; n > 0; n--) {
+		/* Swap in a new block into a slot */
+		for (i = 0; i < N; i++) {
+			unsigned int bin = rte_rand_max(n);
+
+			sz = rte_rand_max(1024) + 1;
+			p1 = rte_zmalloc("swap", sz, 0);
+			if (!p1){
+				printf("rte_zmalloc(%zu) returned NULL (i=%u)\n", sz, i);
+				goto fail;
+			}
+
+			if (!is_all_zero(p1, sz)) {
+				printf("rte_zmalloc didn't zero the allocated memory\n");
+				goto fail;
+			}
+
+			rte_free(slots[bin]);
+			slots[bin] = p1;
+		}
+
+		/* Drop last bin */
+		rte_free(slots[n]);
+		slots[n] = NULL;
+	}
+
+	return 0;
+fail:
+	for (i = 0; i < BINS; i++)
+		rte_free(slots[i]);
+
+	return -1;
+}
+
 static int
 test_reordered_free_per_lcore(__rte_unused void *arg)
 {
@@ -1020,6 +1091,21 @@ test_malloc(void)
 	}
 	else printf("test_realloc() passed\n");

+	/*----------------------------*/
+	RTE_LCORE_FOREACH_WORKER(lcore_id) {
+		rte_eal_remote_launch(test_zmalloc, NULL, lcore_id);
+	}
+
+	RTE_LCORE_FOREACH_WORKER(lcore_id) {
+		if (rte_eal_wait_lcore(lcore_id) < 0)
+			ret = -1;
+	}
+	if (ret < 0){
+		printf("test_zmalloc() failed\n");
+		return ret;
+	}
+	else printf("test_zmalloc() passed\n");
+
 	/*----------------------------*/
 	RTE_LCORE_FOREACH_WORKER(lcore_id) {
 		rte_eal_remote_launch(test_align_overlap_per_lcore, NULL, lcore_id);