From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 0816DA034F; Wed, 24 Feb 2021 14:33:19 +0100 (CET) Received: from [217.70.189.124] (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id AA5A51607BE; Wed, 24 Feb 2021 14:33:18 +0100 (CET) Received: from mail-il1-f174.google.com (mail-il1-f174.google.com [209.85.166.174]) by mails.dpdk.org (Postfix) with ESMTP id 3F6D94069B for ; Wed, 24 Feb 2021 14:33:17 +0100 (CET) Received: by mail-il1-f174.google.com with SMTP id q9so1723922ilo.1 for ; Wed, 24 Feb 2021 05:33:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=/+QCMLEHxdg6xY6eOrBmwQcbAF4nxWWdZf7+iVVR8pw=; b=Mf/eiphDjNCBBZHllO5rU1pkGL1p5uiPzfafeReP+MoARW7qFyifIuozFwtuboN2we aH9bGz5bA5Z6JG+t416KnISDu90KWDzAv9uXbH6+0jEM+178s6ZgxdLMcRjkzVb1KPwR KcP2nULcOpPBa0Bs4k6pLxEecHybzF30dRGGbtfbHQDLJCYFrZBQiLl8/Lh08h+PBcHE zJbAX84cdAAByt7/URVScP+t5ZJVKtILJt7nrIG0GQ7IU/DSqKU7Cy9C5eFOKVN67QBJ vpMALR8gNck9xRBOUczI7fiLk7b1WNuRGUtSgZCC3TwKMQFMrTgIoXH/pfGe2c+AmTwI ZzMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=/+QCMLEHxdg6xY6eOrBmwQcbAF4nxWWdZf7+iVVR8pw=; b=UqOaOqTAx0zoaz7HJi42dZvmRNr+sh2O4PrendrPw4VED7/vw0te5ophHrRDwx+v0w NanCQw38Sz17aeyQ35mCbA+Zsqz4GcgFtYGgdm46/Z9RYtBYXzpyxcFKN5a2PQYNY70K rv8nWXaDlhiCkJxcMzeNGhs8uMu2eTpBgr+8OpQxLCsd6AdaPbdmjL8yWhwwRerb5byA 3jZVjGhatPJHR7Dqc6T/G7vl5/UaLFKmAvSVzkrBMNJ2KeEagUvUXm5GUTAgstAHd1yo afp0KOIDgShO9iharwfTdEX9XZwum7bQDuOUoQLSLjoNZsV8rNWozzpt+IMriSt+fHcp FSyQ== X-Gm-Message-State: AOAM533Yi6ujMccjDUhwm2WLo4nc00CXiU3d8kX68ZCcGInHzjEDhVeH WzthN9YBYhruAJGQrMDTkhNs0aCq4Rjw5Z2upqc= X-Google-Smtp-Source: ABdhPJzQw0dE7780TO6X3Upnx5LIZRGnpa3zcSdcSBA4Mv6y50oSHGf690ucJxmx39hLLMiBB8DTu2SGu+SzwVgvN3E= X-Received: by 2002:a92:ad0a:: with SMTP id w10mr23106369ilh.235.1614173596512; Wed, 24 Feb 2021 05:33:16 -0800 (PST) MIME-Version: 1.0 References: <20201126144613.4986-1-eladv6@gmail.com> <20210223134504.699-1-eladv6@gmail.com> In-Reply-To: From: Elad Nachman Date: Wed, 24 Feb 2021 15:33:05 +0200 Message-ID: To: Igor Ryzhov Cc: Ferruh Yigit , Stephen Hemminger , dev Content-Type: text/plain; charset="UTF-8" Subject: Re: [dpdk-dev] [PATCH 2/2] kni: fix rtnl deadlocks and race conditions v3 X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 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 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 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 >> --- >> 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 >>