Re: [dpdk-dev] [PATCH] eal/freebsd: lock memory device to prevent conflicts

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 13-Sep-21 2:36 PM, Bruce Richardson wrote:
> On Mon, Sep 13, 2021 at 02:14:55PM +0100, Burakov, Anatoly wrote:
>> On 13-Sep-21 12:06 PM, Bruce Richardson wrote:
>>> Only a single DPDK process on the system can be using the /dev/contigmem
>>> mappings at a time, but this was never explicitly enforced, e.g. when
>>> using --in-memory flag on two processes. To prevent possible conflict
>>> issues, we lock the dev node when it's in use, preventing other DPDK
>>> processes from starting up and causing problems for us.
>>>
>>> Fixes: 764bf26873b9 ("add FreeBSD support")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
>>> ---
>>>    lib/eal/freebsd/eal_hugepage_info.c | 4 ++++
>>>    1 file changed, 4 insertions(+)
>>>
>>> diff --git a/lib/eal/freebsd/eal_hugepage_info.c b/lib/eal/freebsd/eal_hugepage_info.c
>>> index 408f054f7a..4a8d87c23e 100644
>>> --- a/lib/eal/freebsd/eal_hugepage_info.c
>>> +++ b/lib/eal/freebsd/eal_hugepage_info.c
>>> @@ -90,6 +90,10 @@ eal_hugepage_info_init(void)
>>>    		RTE_LOG(ERR, EAL, "could not open "CONTIGMEM_DEV"\n");
>>>    		return -1;
>>>    	}
>>> +	if (flock(fd, LOCK_EX) < 0) {
>>> +		RTE_LOG(ERR, EAL, "could not lock memory. Is another DPDK process running?\n");
>>> +		return -1;
>>> +	}
>>>    	if (buffer_size >= 1<<30)
>>>    		RTE_LOG(INFO, EAL, "Contigmem driver has %d buffers, each of size %dGB\n",
>>>
>>
>> This only gets triggered when regular init path is chosen, i.e. --no-huge
>> still works.
> 
> Yes, but that is ok, I think, since no-huge doesn't use these resources or
> suffer from this problem. On the other hand, except for running unit tests,
> no-huge mode is pretty useless on FreeBSD as we don't have any
> vfio-equivalent support, so all HW access has to use physical addresses
> which can only be got using contigmem.

What i meant to say was, i've checked this against '--no-huge' which 
*should* still work with this patch, and it does :) So, the phrasing was 
unfortunate, but we agree!

> 
>> I'm a bit uneasy with --in-memory mode pretending to work on
>> FreeBSD and Windows, but that's a separate problem :)
> 
> Yes, it is, though one that does belong is the same area as this one. The
> "fix" is probably to just print a warning when --in-memory is used,
> informing the user that the flag is ignored and then continue.
> Alternatively we can error out, but I think the warn+continue is better,
> myself.

I think erroring out is better. The feature is intended to work a 
certain way, so if we can't guarantee that it does, we can't pretend it 
is "supported" or "is working". But again, irrelevant to this patch :)

> 
>> As far as the patch
>> goes, the problem it addresses does get fixed.
>>
>> Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>
>>
> Thanks.
> 
> /Bruce
> 


-- 
Thanks,
Anatoly