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From: Igor Ryzhov <iryzhov@nfware.com>
To: Elad Nachman <eladv6@gmail.com>
Cc: Ferruh Yigit <ferruh.yigit@intel.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	dev <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 2/2] kni: fix rtnl deadlocks and race conditions v3
Date: Wed, 24 Feb 2021 19:31:37 +0300
Message-ID: <CAF+s_FwtxydNiG+cFcDfPStBB39TTwQhcxGcW7PsrR=gbwGeNQ@mail.gmail.com> (raw)
In-Reply-To: <CACXF7qkhkzFc-=v=iiBzh2V7rLjk1U34VUfPbNrnYJND_0TKHQ@mail.gmail.com>

Elad,

To make it work on Mellanox NIC, you need to find a way to send
ALL requests to userspace without rtnl_lock held, including link down.
As I understand, the race condition in __dev_close_many must be
solved somehow.

I can't provide remote access, but I am happy to test on Mellanox NICs,
if you find a way to fix link down requests.

On Wed, Feb 24, 2021 at 7:11 PM Elad Nachman <eladv6@gmail.com> wrote:

> Sorry, don't have Mellanox NIC currently. Will have one in 8-12 weeks.
> Will be happy to test it remotely if anyone can provide remote HW or
> VM (Azure, for example).
>
> Elad.
>
> On Wed, Feb 24, 2021 at 5:18 PM Igor Ryzhov <iryzhov@nfware.com> wrote:
> >
> > Stephen's idea was to fix the deadlock when working with the bifurcated
> driver.
> > Your rework breaks this because you still send link down requests under
> rtnl_lock.
> > Did you test your patch with Mellanox devices?
> >
> > On Wed, Feb 24, 2021 at 5:56 PM Elad Nachman <eladv6@gmail.com> wrote:
> >>
> >> The deadlock scenarios are explained below:
> >>
> >> It is described in Stephen Hemminger's original patch:
> >>
> >> "
> >>
> >> This fixes a deadlock when using KNI with bifurcated drivers.
> >> Bringing kni device up always times out when using Mellanox
> >> devices.
> >>
> >> The kernel KNI driver sends message to userspace to complete
> >> the request. For the case of bifurcated driver, this may involve
> >> an additional request to kernel to change state. This request
> >> would deadlock because KNI was holding the RTNL mutex.
> >>
> >> "
> >>
> >> And also in my patch:
> >>
> >> "
> >> 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.
> >> "
> >>
> >> FYI,
> >>
> >> Elad.
> >>
> >> On Wed, Feb 24, 2021 at 4:41 PM Igor Ryzhov <iryzhov@nfware.com> wrote:
> >> >
> >> > Both link up and link down also work for me without this patch.
> >> > So what's the point in merging it?
> >> >
> >> > Just to clarify - I am not against the idea of this patch.
> >> > Talking to userspace under rtnl_lock is a bad idea.
> >> > I just think that any patch should fix some specified problem.
> >> >
> >> > If this patch is trying to solve the overall "userspace request under
> rtnl_lock" problem,
> >> > then it doesn't solve it correctly, because we still send link down
> requests under the lock.
> >> >
> >> > If this patch is trying to solve some other issue, for example, some
> "KNI deadlocks"
> >> > you're talking about, then you should explain what these deadlocks
> are, how to reproduce
> >> > them and why this patch solves the issue.
> >> >
> >> > On Wed, Feb 24, 2021 at 5:07 PM Elad Nachman <eladv6@gmail.com>
> wrote:
> >> >>
> >> >> I tested both link up and link down many times without any problems
> on
> >> >> 100 restarts of the application.
> >> >>
> >> >> Having KNI deadlock frequently for real life applications is far
> worst, IMHO.
> >> >>
> >> >> FYI
> >> >>
> >> >> Elad.
> >> >>
> >> >> On Wed, Feb 24, 2021 at 4:04 PM Igor Ryzhov <iryzhov@nfware.com>
> wrote:
> >> >> >
> >> >> > Elad,
> >> >> >
> >> >> > I understand your point.
> >> >> > But the fact that this fix works for you doesn't mean that it will
> work for all DPDK users.
> >> >> >
> >> >> > For example, I provided two simple commands: "ip link set up" and
> "ip link set down".
> >> >> > Your fix works for only one of them. For me, this is not a proper
> fix.
> >> >> > It may work for you because you don't disable interfaces, but it
> will fail for users who do.
> >> >> >
> >> >> > On Wed, Feb 24, 2021 at 4:33 PM Elad Nachman <eladv6@gmail.com>
> wrote:
> >> >> >>
> >> >> >> Currently KNI has a lot of issues with deadlocks locking the code,
> >> >> >> after this commit, they are gone, and the code runs properly
> without
> >> >> >> crashing.
> >> >> >> That was tested with over 100 restarts of the application, which
> >> >> >> previously required a hard reset of the board.
> >> >> >>
> >> >> >> I think this benefit overweights the complication of the code.
> >> >> >>
> >> >> >> The function is called with rtnl locked because this is how the
> Linux
> >> >> >> kernel is designed to work - it is not designed to work with
> deferral
> >> >> >> to user-space mid-function.
> >> >> >>
> >> >> >> To fix all such requests you need to reach an agreement with Linux
> >> >> >> netdev, which is unlikely.
> >> >> >>
> >> >> >> Calling user-space can be done asynchronously, as Ferruh asked,
> but
> >> >> >> then you will always have to return success, even on failure, as
> Linux
> >> >> >> kernel does not have a mechanism to asynchronously report on
> failure
> >> >> >> for such system calls.
> >> >> >>
> >> >> >> IMHO - weighting the non-reporting of failure versus how the code
> >> >> >> looks (as it functions perfectly OK), I decided to go with
> >> >> >> functionality.
> >> >> >>
> >> >> >> FYI,
> >> >> >>
> >> >> >> Elad.
> >> >> >>
> >> >> >> On Wed, Feb 24, 2021 at 2:50 PM Igor Ryzhov <iryzhov@nfware.com>
> wrote:
> >> >> >> >
> >> >> >> > This looks more like a hack than an actual fix to me.
> >> >> >> >
> >> >> >> > After this commit:
> >> >> >> > "ip link set up" is sent to the userspace with unlocked
> rtnl_lock
> >> >> >> > "ip link set down" is sent to the userspace with locked
> rtnl_lock
> >> >> >> >
> >> >> >> > How is this really fixing anything? IMHO it only complicates
> the code.
> >> >> >> > If talking with userspace under rtnl_lock is a problem, then we
> should fix all such requests, not only part of them.
> >> >> >> > If it is not a problem, then I don't see any point in merging
> this.
> >> >> >> >
> >> >> >> > On Tue, Feb 23, 2021 at 4:45 PM Elad Nachman <eladv6@gmail.com>
> wrote:
> >> >> >> >>
> >> >> >> >> This part of the series includes my fixes for the issues
> reported
> >> >> >> >> by Ferruh and Igor 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.
> >> >> >> >>
> >> >> >> >> Signed-off-by: Elad Nachman <eladv6@gmail.com>
> >> >> >> >> ---
> >> >> >> >> 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 | 29 +++++++++++++++++++++--------
> >> >> >> >>  1 file changed, 21 insertions(+), 8 deletions(-)
> >> >> >> >>
> >> >> >> >> diff --git a/kernel/linux/kni/kni_net.c
> b/kernel/linux/kni/kni_net.c
> >> >> >> >> index f0b6e9a8d..017e44812 100644
> >> >> >> >> --- a/kernel/linux/kni/kni_net.c
> >> >> >> >> +++ b/kernel/linux/kni/kni_net.c
> >> >> >> >> @@ -110,9 +110,26 @@ 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;
> >> >> >> >>
> >> >> >> >>         ASSERT_RTNL();
> >> >> >> >>
> >> >> >> >> +       /* Since we need to wait and RTNL mutex is held
> >> >> >> >> +        * drop the mutex and hold reference to keep device
> >> >> >> >> +        */
> >> >> >> >> +       if (!req_is_dev_stop) {
> >> >> >> >> +               dev_hold(dev);
> >> >> >> >> +               rtnl_unlock();
> >> >> >> >> +       }
> >> >> >> >> +
> >> >> >> >>         mutex_lock(&kni->sync_lock);
> >> >> >> >>
> >> >> >> >>         /* Construct data */
> >> >> >> >> @@ -124,16 +141,8 @@ kni_net_process_request(struct net_device
> *dev, struct rte_kni_request *req)
> >> >> >> >>                 goto fail;
> >> >> >> >>         }
> >> >> >> >>
> >> >> >> >> -       /* Since we need to wait and RTNL mutex is held
> >> >> >> >> -        * drop the mutex and hold refernce to keep device
> >> >> >> >> -        */
> >> >> >> >> -       dev_hold(dev);
> >> >> >> >> -       rtnl_unlock();
> >> >> >> >> -
> >> >> >> >>         ret_val = wait_event_interruptible_timeout(kni->wq,
> >> >> >> >>                         kni_fifo_count(kni->resp_q), 3 * HZ);
> >> >> >> >> -       rtnl_lock();
> >> >> >> >> -       dev_put(dev);
> >> >> >> >>
> >> >> >> >>         if (signal_pending(current) || ret_val <= 0) {
> >> >> >> >>                 ret = -ETIME;
> >> >> >> >> @@ -152,6 +161,10 @@ kni_net_process_request(struct net_device
> *dev, struct rte_kni_request *req)
> >> >> >> >>
> >> >> >> >>  fail:
> >> >> >> >>         mutex_unlock(&kni->sync_lock);
> >> >> >> >> +       if (!req_is_dev_stop) {
> >> >> >> >> +               rtnl_lock();
> >> >> >> >> +               dev_put(dev);
> >> >> >> >> +       }
> >> >> >> >>         return ret;
> >> >> >> >>  }
> >> >> >> >>
> >> >> >> >> --
> >> >> >> >> 2.17.1
> >> >> >> >>
>

  parent reply	other threads:[~2021-02-24 16:31 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-26 14:46 [dpdk-dev] [PATCH] kni: fix rtnl deadlocks and race conditions Elad Nachman
2021-02-19 18:41 ` Ferruh Yigit
2021-02-21  8:03   ` Elad Nachman
2021-02-22 15:58     ` Ferruh Yigit
2021-02-23 12:05 ` [dpdk-dev] [PATCH V2] kni: fix rtnl deadlocks and race conditions v2 Elad Nachman
2021-02-23 12:53   ` Ferruh Yigit
2021-02-23 13:44 ` [dpdk-dev] [PATCH 1/2] kni: fix rtnl deadlocks and race conditions v3 Elad Nachman
2021-02-23 13:45 ` [dpdk-dev] [PATCH 2/2] " Elad Nachman
2021-02-24 12:49   ` Igor Ryzhov
2021-02-24 13:33     ` Elad Nachman
2021-02-24 14:04       ` Igor Ryzhov
2021-02-24 14:06         ` Elad Nachman
2021-02-24 14:41           ` Igor Ryzhov
2021-02-24 14:56             ` Elad Nachman
2021-02-24 15:18               ` Igor Ryzhov
     [not found]                 ` <CACXF7qkhkzFc-=v=iiBzh2V7rLjk1U34VUfPbNrnYJND_0TKHQ@mail.gmail.com>
2021-02-24 16:31                   ` Igor Ryzhov [this message]
2021-02-24 15:54     ` Stephen Hemminger
2021-02-25 14:32 ` [dpdk-dev] [PATCH 1/2] kni: fix kernel deadlock when using mlx devices Elad Nachman
2021-02-25 14:32   ` [dpdk-dev] [PATCH 2/2] kni: fix rtnl deadlocks and race conditions v4 Elad Nachman
2021-02-25 21:01     ` Igor Ryzhov
2021-02-26 15:48       ` Stephen Hemminger
2021-02-26 17:43         ` Elad Nachman
2021-03-01  8:10           ` Igor Ryzhov
2021-03-01 16:38             ` Stephen Hemminger
2021-03-15 16:58               ` Ferruh Yigit
2021-03-01 20:27             ` Dan Gora
2021-03-01 21:26               ` Dan Gora
2021-03-02 16:44                 ` Elad Nachman
2021-03-15 17:17     ` Ferruh Yigit
2021-03-16 18:35       ` Elad Nachman
2021-03-16 18:42         ` Ferruh Yigit
2021-03-15 17:17   ` [dpdk-dev] [PATCH 1/2] kni: fix kernel deadlock when using mlx devices Ferruh Yigit
2021-03-29 14:36 ` [dpdk-dev] [PATCH v5 1/3] kni: refactor user request processing Ferruh Yigit
2021-03-29 14:36   ` [dpdk-dev] [PATCH v5 2/3] kni: support async user request Ferruh Yigit
2021-03-29 14:36   ` [dpdk-dev] [PATCH v5 3/3] kni: fix kernel deadlock when using mlx devices Ferruh Yigit
2021-04-09 14:56     ` [dpdk-dev] [dpdk-stable] " Ferruh Yigit
2021-04-12 14:35       ` Elad Nachman
2021-04-20 23:07         ` Thomas Monjalon
2021-04-23  8:41           ` Igor Ryzhov
2021-04-23  8:59             ` Ferruh Yigit
2021-04-23 12:43               ` Igor Ryzhov
2021-04-23 12:58                 ` Igor Ryzhov

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