Re: [PATCH] eal: zero out new added memory

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

2022-08-27 09:25 (UTC+0000), chengtcli@qq.com:
> From: lic121 <lic121@chinatelecom.cn>
> 
> When RTE_MALLOC_DEBUG not configured, rte_zmalloc_socket() doens't
> zero oute allocaed memory. Because memory are zeroed out when free
> in malloc_elem_free(). But seems the initial allocated memory is
> not zeroed out as expected.
> 
> This patch zero out initial allocated memory in
> malloc_heap_add_memory().
> 
> With dpdk 20.11.5, "QLogic Corp. FastLinQ QL41000" probe triggers
> this problem.
> ```
>   Stack trace of thread 412780:
>   #0  0x0000000000e5fb99 ecore_int_igu_read_cam (dpdk-testpmd)
>   #1  0x0000000000e4df54 ecore_get_hw_info (dpdk-testpmd)
>   #2  0x0000000000e504aa ecore_hw_prepare (dpdk-testpmd)
>   #3  0x0000000000e8a7ca qed_probe (dpdk-testpmd)
>   #4  0x0000000000e83c59 qede_common_dev_init (dpdk-testpmd)
>   #5  0x0000000000e84c8e qede_eth_dev_init (dpdk-testpmd)
>   #6  0x00000000009dd5a7 rte_pci_probe_one_driver (dpdk-testpmd)
>   #7  0x00000000009734e3 rte_bus_probe (dpdk-testpmd)
>   #8  0x00000000009933bd rte_eal_init (dpdk-testpmd)
>   #9  0x000000000041768f main (dpdk-testpmd)
>   #10 0x00007f41a7001b17 __libc_start_main (libc.so.6)
>   #11 0x000000000067e34a _start (dpdk-testpmd)
> ```
> 
> Signed-off-by: lic121 <lic121@chinatelecom.cn>
> ---
>  lib/librte_eal/common/malloc_heap.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/lib/librte_eal/common/malloc_heap.c b/lib/librte_eal/common/malloc_heap.c
> index f4e20ea..1607401 100644
> --- a/lib/librte_eal/common/malloc_heap.c
> +++ b/lib/librte_eal/common/malloc_heap.c
> @@ -96,11 +96,19 @@
>  		void *start, size_t len)
>  {
>  	struct malloc_elem *elem = start;
> +	void *ptr;
> +	size_t data_len
> +
>  
>  	malloc_elem_init(elem, heap, msl, len, elem, len);
>  
>  	malloc_elem_insert(elem);
>  
> +	/* Zero out new added memory. */
> +	*ptr = RTE_PTR_ADD(elem, MALLOC_ELEM_HEADER_LEN);
> +	data_len = elem->size - MALLOC_ELEM_OVERHEAD;
> +	memset(ptr, 0, data_len);
> +
>  	elem = malloc_elem_join_adjacent_free(elem);
>  
>  	malloc_elem_free_list_insert(elem);

Hi,

The kernel ensures that the newly mapped memory is zeroed,
and DPDK ensures that files in hugetlbfs are not re-mapped.
What makes you think that it is not zeroed?
Were you able to catch [start; start+len) contain non-zero bytes
at the start of this function?
If so, is it system memory (not an external heap)?
If so, what is the CPU, kernel, any custom settings?

Can it be the PMD or the app that uses rte_malloc instead of rte_zmalloc?

This patch cannot be accepted as-is anyway:
1. It zeroes memory even if the code was called not via rte_zmalloc().
2. It leads to zeroing on both alloc and free, which is suboptimal.