Re: [dpdk-dev] [PATCH] eal/linux: add operation LOCK_NB to flock()

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 15 Apr 2021 15:24:01 +0100
"Burakov, Anatoly" <anatoly.burakov@intel.com> wrote:

> On 25-Mar-21 8:21 AM, xiangxia.m.yue@gmail.com wrote:
> > From: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> > 
> > The hugepage of different size, 2MB, 1GB may be mounted on
> > the same directory (e.g /dev/hugepages). Then dpdk
> > primary process will be blocked. To address this issue,
> > add the LOCK_NB flags to flock().
> > 
> > $ cat /proc/mounts
> > ...
> > none /dev/hugepages hugetlbfs rw,seclabel,relatime,pagesize=1024M 0 0
> > none /dev/hugepages hugetlbfs rw,seclabel,relatime,pagesize=2M 0 0
> > 
> > Add more details for err logs.
> > 
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
> > ---
> >   lib/librte_eal/linux/eal_hugepage_info.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/lib/librte_eal/linux/eal_hugepage_info.c b/lib/librte_eal/linux/eal_hugepage_info.c
> > index d97792cadeb6..1ff76e539053 100644
> > --- a/lib/librte_eal/linux/eal_hugepage_info.c
> > +++ b/lib/librte_eal/linux/eal_hugepage_info.c
> > @@ -451,9 +451,12 @@ hugepage_info_init(void)
> >   		hpi->lock_descriptor = open(hpi->hugedir, O_RDONLY);
> >   
> >   		/* if blocking lock failed */
> > -		if (flock(hpi->lock_descriptor, LOCK_EX) == -1) {
> > +		if (flock(hpi->lock_descriptor, LOCK_EX | LOCK_NB) == -1) {
> >   			RTE_LOG(CRIT, EAL,
> > -				"Failed to lock hugepage directory!\n");
> > +				"Failed to lock hugepage directory! "
> > +				"The hugepage dir (%s) was locked by "
> > +				"other processes or self twice.\n",
> > +				hpi->hugedir);
> >   			break;
> >   		}
> >   		/* clear out the hugepages dir from unused pages */
> >   
> 
> Use cases such as "having two hugetlbfs page sizes on the same hugetlbfs 
> mountpoint" are user error, but i agree that deadlocking is probably not 
> the way we want to go about it.
> 
> An alternative way would be to check if we already have a mountpoint 
> with the same path, and this would produce a better error message (as a 
> user, "hugepage dir is locked by self twice" doesn't tell me anything 
> useful), at a cost of slightly more complicated code.
> 
> I'm not sure which way i want to go here. Normally, hugetlbfs shouldn't 
> be staying locked for long, so i'm wary of adding a LOCK_NB here, so i 
> feel slightly uneasy about this patch. Do you have any opinions?
> 
> Also, do other OS's EALs need similar fix?
> 

Dropping this patch. It is one of those:
"It hurts when I do this stupid thing" patches.