Re: [dpdk-dev] [PATCH 2/2] kni: fix rtnl deadlocks and race conditions v4

[Elad Nachman <eladv6@gmail.com>]

Hi,

Owing to my current development schedule and obligations, I see no
opportunity to make this set of changes in the near future.

Sorry,

Elad.

בתאריך יום ב׳, 15 במרץ 2021, 19:17, מאת Ferruh Yigit ‏<
ferruh.yigit@intel.com>:

> On 2/25/2021 2:32 PM, Elad Nachman wrote:
> > This part of the series includes my fixes for the issues reported
> > by Ferruh and Igor (and Igor comments for v3 of the patch)
> > on top of part 1 of the patch series:
> >
> > A. KNI sync lock is being locked while rtnl is held.
> > If two threads are calling kni_net_process_request() ,
> > then the first one will take the sync lock, release rtnl lock then sleep.
> > The second thread will try to lock sync lock while holding rtnl.
> > The first thread will wake, and try to lock rtnl, resulting in a
> deadlock.
> > The remedy is to release rtnl before locking the KNI sync lock.
> > Since in between nothing is accessing Linux network-wise,
> > no rtnl locking is needed.
> >
> > B. There is a race condition in __dev_close_many() processing the
> > close_list while the application terminates.
> > It looks like if two vEth devices are terminating,
> > and one releases the rtnl lock, the other takes it,
> > updating the close_list in an unstable state,
> > causing the close_list to become a circular linked list,
> > hence list_for_each_entry() will endlessly loop inside
> > __dev_close_many() .
> > Since the description for the original patch indicate the
> > original motivation was bringing the device up,
> > I have changed kni_net_process_request() to hold the rtnl mutex
> > in case of bringing the device down since this is the path called
> > from __dev_close_many() , causing the corruption of the close_list.
> > In order to prevent deadlock in Mellanox device in this case, the
> > code has been modified not to wait for user-space while holding
> > the rtnl lock.
> > Instead, after the request has been sent, all locks are relinquished
> > and the function exits immediately with return code of zero (success).
> >
> > To summarize:
> > request != interface down : unlock rtnl, send request to user-space,
> > wait for response, send the response error code to caller in user-space.
> >
> > request == interface down: send request to user-space, return immediately
> > with error code of 0 (success) to user-space.
> >
> > Signed-off-by: Elad Nachman <eladv6@gmail.com>
> >
> >
> > ---
> > v4:
> > * for if down case, send asynchronously with rtnl locked and without
> >    wait, returning immediately to avoid both kernel race conditions
> >    and deadlock in user-space
> > v3:
> > * Include original patch and new patch as a series of patch, added a
> >    comment to the new patch
> > v2:
> > * rebuild the patch as increment from patch 64106
> > * fix comment and blank lines
> > ---
> >   kernel/linux/kni/kni_net.c      | 41 +++++++++++++++++++++++++++------
> >   lib/librte_kni/rte_kni.c        |  7 ++++--
> >   lib/librte_kni/rte_kni_common.h |  1 +
> >   3 files changed, 40 insertions(+), 9 deletions(-)
> >
> > diff --git a/kernel/linux/kni/kni_net.c b/kernel/linux/kni/kni_net.c
> > index f0b6e9a8d..ba991802b 100644
> > --- a/kernel/linux/kni/kni_net.c
> > +++ b/kernel/linux/kni/kni_net.c
> > @@ -110,12 +110,34 @@ kni_net_process_request(struct net_device *dev,
> struct rte_kni_request *req)
> >       void *resp_va;
> >       uint32_t num;
> >       int ret_val;
> > +     int req_is_dev_stop = 0;
> > +
> > +     /* For configuring the interface to down,
> > +      * rtnl must be held all the way to prevent race condition
> > +      * inside __dev_close_many() between two netdev instances of KNI
> > +      */
> > +     if (req->req_id == RTE_KNI_REQ_CFG_NETWORK_IF &&
> > +                     req->if_up == 0)
> > +             req_is_dev_stop = 1;
>
> Having this request type checks in the 'kni_net_process_request()'
> function
> looks like hack.
> Since adding a new field into the "struct rte_kni_request", that can be a
> more
> generic 'asnyc' field, and the requested function, like
> 'kni_net_release()' can
> set it to support async requests.
>
> And can you please separate the function to add a more generic async
> request
> support on its patch, which should do:
> - add new 'asnyc' field to "struct rte_kni_request"
> - in 'kni_net_process_request()', if 'req->async' set, do not wait for
> response
> - in library, 'lib/librte_kni/rte_kni.c', in 'rte_kni_handle_request()'
> function, if the request is async don't put the response
> (These are already done in this patch)
>
> Overall it can be three patch set:
> 1) Function parameter change
> 2) Add generic async request support (with documentation update)
> 3) rtnl unlock and make 'kni_net_release()' request async (actual fix)
> (We can discuss more if to make 'kni_net_release()' async with a kernel
> parameter or not)
>
> What do you think, does it make sense?
>
>