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

["Morten Brørup" <mb@smartsharesystems.com>]

> From: David Marchand [mailto:david.marchand@redhat.com]
> Sent: Monday, 29 August 2022 13.58
> 
> On Mon, Aug 29, 2022 at 1:38 PM lic121 <chengtcli@qq.com> wrote:
> >
> > On Mon, Aug 29, 2022 at 01:18:36AM +0000, lic121 wrote:
> > > 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().
> > > > > > >

[...]

> > > > > > Hi,
> > > > > >
> > > > > > The kernel ensures that the newly mapped memory is zeroed,
> > > > > > and DPDK ensures that files in hugetlbfs are not re-mapped.

David, are you suggesting that this invariant - guaranteeing that DPDK memory is zeroed - was violated by SELinux in the SELinux/container issue you were tracking?

If so, the method to ensure the invariant is faulty for SELinux. Assuming DPDK supports SELinux, this bug should be fixed.

> > > > > > 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_p
> ci.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
> >
> > Today we probaly meet the same issue with intel E810 nic, the behave
> is
> > that E810 nic can be probed on some host, but can't one some other.
> On
> > the same host, one E810 may be probed while the other one can't be.
> > After I applied this patch, no such issue anymore.
> 
> Are you perhaps running your DPDK application from inside a container?
> I remember tracking an issue which had to do with reusing a "dirty"
> hugepage file (because of SELinux forbidding to destroy those files).
> 
> 
> --
> David Marchand
>