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

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

2022-08-27 13:31 (UTC+0000), lic121:
> 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

Sorry, it seems that something is wrong with your debug.
Your link is for 20.11.0.
In 20.11.5 (apparently always) struct qede_dev::edev is not a pointer [2].
Even if it was, in zeroed memory it would be a NULL pointer,
reading a member would give a random value at NULL + some offset.
I suggest to print content of the allocated memory with rte_hexdump().

[2]:
http://git.dpdk.org/dpdk-stable/tree/drivers/net/qede/qede_ethdev.h?h=v20.11.5#n223