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

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/16/2021 6:35 PM, Elad Nachman wrote:
> Hi,
> 
> Owing to my current development schedule and obligations, I see no opportunity 
> to make this set of changes in the near future.
> 

I can do on top of your work if you don't mind?

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