Re: [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask

["Lin, Xueqin" <xueqin.lin@intel.com>]

Hi Lucero,

No, we have reproduced multi-process issues(include symmetric_mp, simple_mp, hotplug_mp, multi-process unit test… )on most of our servers.
It is also strange that 1~2 servers don’t have the issue.

Bind two NNT ports or FVL ports

./build/symmetric_mp -c 4 --proc-type=auto -- -p 3 --num-procs=4 --proc-id=1

EAL: Detected 88 lcore(s)
EAL: Detected 2 NUMA nodes
EAL: Auto-detected process type: SECONDARY
[New Thread 0x7ffff6eda700 (LWP 90103)]
EAL: Multi-process socket /var/run/dpdk/rte/mp_socket_90099_2f1b553882b62
[New Thread 0x7ffff66d9700 (LWP 90104)]

Thread 1 "symmetric_mp" received signal SIGSEGV, Segmentation fault.
0x00000000005566b5 in rte_fbarray_find_next_used ()
(gdb) bt
#0  0x00000000005566b5 in rte_fbarray_find_next_used ()
#1  0x000000000054da9c in rte_eal_check_dma_mask ()
#2  0x0000000000572ae7 in pci_one_device_iommu_support_va ()
#3  0x0000000000573988 in rte_pci_get_iommu_class ()
#4  0x000000000054f743 in rte_bus_get_iommu_class ()
#5  0x000000000053c123 in rte_eal_init ()
#6  0x000000000046be2b in main ()

Best regards,
Xueqin

From: Alejandro Lucero [mailto:alejandro.lucero@netronome.com]
Sent: Tuesday, October 30, 2018 5:41 PM
To: Lin, Xueqin <xueqin.lin@intel.com>
Cc: Yao, Lei A <lei.a.yao@intel.com>; Thomas Monjalon <thomas@monjalon.net>; dev <dev@dpdk.org>; Xu, Qian Q <qian.q.xu@intel.com>; Burakov, Anatoly <anatoly.burakov@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>
Subject: Re: [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask


On Tue, Oct 30, 2018 at 3:20 AM Lin, Xueqin <xueqin.lin@intel.com<mailto:xueqin.lin@intel.com>> wrote:
Hi Lucero&Thomas,

Find the patch can’t fix multi-process cases.

Hi,

I think it is not specifically about multiprocess but about hotplug with multiprocess because I can execute the symmetric_mp successfully with a secondary process.

Working on this as a priority.

Thanks.

Steps:

1.       Setup primary process successfully

./hotplug_mp --proc-type=auto



2.       Fail to setup secondary process

./hotplug_mp --proc-type=auto

EAL: Detected 88 lcore(s)

EAL: Detected 2 NUMA nodes

EAL: Auto-detected process type: SECONDARY

EAL: Multi-process socket /var/run/dpdk/rte/mp_socket_147212_2bfe08ee88d23

Segmentation fault (core dumped)


More information as below:

Thread 1 "hotplug_mp" received signal SIGSEGV, Segmentation fault.

0x0000000000597cfb in find_next (arr=0x7ffff7ff20a4, start=0, used=true)

    at /root/dpdk/lib/librte_eal/common/eal_common_fbarray.c:264

264             for (idx = first; idx < msk->n_masks; idx++) {

#0  0x0000000000597cfb in find_next (arr=0x7ffff7ff20a4, start=0, used=true)

    at /root/dpdk/lib/librte_eal/common/eal_common_fbarray.c:264

#1  0x0000000000598573 in fbarray_find (arr=0x7ffff7ff20a4, start=0, next=true,

    used=true) at /root/dpdk/lib/librte_eal/common/eal_common_fbarray.c:1001

#2  0x000000000059929b in rte_fbarray_find_next_used (arr=0x7ffff7ff20a4, start=0)

    at /root/dpdk/lib/librte_eal/common/eal_common_fbarray.c:1018

#3  0x000000000058c877 in rte_memseg_walk_thread_unsafe (func=0x58c401 <check_iova>,

    arg=0x7fffffffcc38) at /root/dpdk/lib/librte_eal/common/eal_common_memory.c:589

#4  0x000000000058ce08 in rte_eal_check_dma_mask (maskbits=48 '0')

    at /root/dpdk/lib/librte_eal/common/eal_common_memory.c:465

#5  0x00000000005b96c4 in pci_one_device_iommu_support_va (dev=0x11b3d90)

    at /root/dpdk/drivers/bus/pci/linux/pci.c:593

#6  0x00000000005b9738 in pci_devices_iommu_support_va ()

    at /root/dpdk/drivers/bus/pci/linux/pci.c:626

#7  0x00000000005b97a7 in rte_pci_get_iommu_class ()

    at /root/dpdk/drivers/bus/pci/linux/pci.c:650

#8  0x000000000058f1ce in rte_bus_get_iommu_class ()

    at /root/dpdk/lib/librte_eal/common/eal_common_bus.c:237

#9  0x0000000000577c7a in rte_eal_init (argc=2, argv=0x7fffffffdf98)

    at /root/dpdk/lib/librte_eal/linuxapp/eal/eal.c:919

#10 0x000000000045dd56 in main (argc=2, argv=0x7fffffffdf98)

    at /root/dpdk/examples/multi_process/hotplug_mp/main.c:28


Best regards,
Xueqin

From: Alejandro Lucero [mailto:alejandro.lucero@netronome.com<mailto:alejandro.lucero@netronome.com>]
Sent: Monday, October 29, 2018 9:41 PM
To: Yao, Lei A <lei.a.yao@intel.com<mailto:lei.a.yao@intel.com>>
Cc: Thomas Monjalon <thomas@monjalon.net<mailto:thomas@monjalon.net>>; dev <dev@dpdk.org<mailto:dev@dpdk.org>>; Xu, Qian Q <qian.q.xu@intel.com<mailto:qian.q.xu@intel.com>>; Lin, Xueqin <xueqin.lin@intel.com<mailto:xueqin.lin@intel.com>>; Burakov, Anatoly <anatoly.burakov@intel.com<mailto:anatoly.burakov@intel.com>>; Yigit, Ferruh <ferruh.yigit@intel.com<mailto:ferruh.yigit@intel.com>>
Subject: Re: [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask


On Mon, Oct 29, 2018 at 1:18 PM Yao, Lei A <lei.a.yao@intel.com<mailto:lei.a.yao@intel.com>> wrote:


From: Alejandro Lucero [mailto:alejandro.lucero@netronome.com<mailto:alejandro.lucero@netronome.com>]
Sent: Monday, October 29, 2018 8:56 PM
To: Thomas Monjalon <thomas@monjalon.net<mailto:thomas@monjalon.net>>
Cc: Yao, Lei A <lei.a.yao@intel.com<mailto:lei.a.yao@intel.com>>; dev <dev@dpdk.org<mailto:dev@dpdk.org>>; Xu, Qian Q <qian.q.xu@intel.com<mailto:qian.q.xu@intel.com>>; Lin, Xueqin <xueqin.lin@intel.com<mailto:xueqin.lin@intel.com>>; Burakov, Anatoly <anatoly.burakov@intel.com<mailto:anatoly.burakov@intel.com>>; Yigit, Ferruh <ferruh.yigit@intel.com<mailto:ferruh.yigit@intel.com>>
Subject: Re: [dpdk-dev] [PATCH v3 0/6] use IOVAs check based on DMA mask


On Mon, Oct 29, 2018 at 11:46 AM Thomas Monjalon <thomas@monjalon.net<mailto:thomas@monjalon.net>> wrote:
29/10/2018 12:39, Alejandro Lucero:
> I got a patch that solves a bug when calling rte_eal_dma_mask using the
> mask instead of the maskbits. However, this does not solves the deadlock.

The deadlock is a bigger concern I think.

I think once the call to rte_eal_check_dma_mask uses the maskbits instead of the mask, calling rte_memseg_walk_thread_unsafe avoids the deadlock.

Yao, can you try with the attached patch?

Hi, Lucero

This patch can fix the issue at my side. Thanks a lot
for you quick action.


Great!

I will send an official patch with the changes.

I have to say that I tested the patchset, but I think it was where legacy_mem was still there and therefore dynamic memory allocation code not used during memory initialization.

There is something that concerns me though. Using rte_memseg_walk_thread_unsafe could be a problem under some situations although those situations being unlikely.

Usually, calling rte_eal_check_dma_mask happens during initialization. Then it is safe to use the unsafe function for walking memsegs, but with device hotplug and dynamic memory allocation, there exists a potential race condition when the primary process is allocating more memory and concurrently a device is hotplugged and a secondary process does the device initialization. By now, this is just a problem with the NFP, and the potential race condition window really unlikely, but I will work on this asap.

BRs
Lei

> Interestingly, the problem looks like a compiler one. Calling
> rte_memseg_walk does not return when calling inside rt_eal_dma_mask, but if
> you modify the call like this:
>
> -       if (rte_memseg_walk(check_iova, &mask))
> +       if (!rte_memseg_walk(check_iova, &mask))
>
> it works, although the value returned to the invoker changes, of course.
> But the point here is it should be the same behaviour when calling
> rte_memseg_walk than before and it is not.

Anyway, the coding style requires to save the return value in a variable,
instead of nesting the call in an "if" condition.
And the "if" check should be explicitly != 0 because it is not a real boolean.

PS: please do not top post and avoid HTML emails, thanks