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

[lic121 <chengtcli@qq.com>]

On Sat, Aug 27, 2022 at 12:57:50PM +0300, Dmitry Kozlyuk wrote:
> 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.

Hi Dmitry, thanks for the review.

In rte_eth_dev_pci_allocate(), imediately after rte_zmalloc_socket()[1]
I printed
the content in gdb. It's not zero.

print ((struct qede_dev *)(eth_dev->data->dev_private))->edev->p_iov_info

cpu: Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz
kernel: 4.19.90-2102

[1]
https://github.com/DPDK/dpdk/blob/v20.11/lib/librte_ethdev/rte_ethdev_pci.h#L91-L93