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

[lic121 <chengtcli@qq.com>]

On Sat, Aug 27, 2022 at 05:56:54PM +0300, Dmitry Kozlyuk wrote:
> 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().
> 

Sorry I didn't describe my debug clear. At first I debuged with version
20.11.0, I found that the rte_zmalloc_socket() memory is dirty. Then I
tried 20.11.5, I didn't debug on 20.11.5 but the behave is the same(nic
failed to be probed). So in the commit msg I said v20.11.5 has the
issue. But when I describe my debug I uesd 20.11.0 url.

More debug info:
1. I reproduced the issue for tens of times, every time the printed var
has the same value.
2. After search malloc_heap_add_memory, I found that there are 3 places
where call this function to add memory, malloc_add_seg(),
alloc_pages_on_heap() and malloc_heap_add_external_memory(). Firstly, I
zero out memory only for malloc_add_seg(), it didn't fix the issue. Then
I zero out meory in malloc_heap_add_memory() to cover all 3 cases, this
time nic is probed successfully.
3. Once nic is probed, I roll back my fix code, try to reproduce the
issue. But I can't reproduce anymore. So I guess: the memory allocated
when probe qede nic is at a fixed memory location. Because every time in
my debug the printed var has the same value. After I zeroed out the
allocated memory once, I can't reproduce the issue anymore.

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