From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95FFEC4167B for ; Mon, 11 Dec 2023 13:45:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234350AbjLKNpn (ORCPT ); Mon, 11 Dec 2023 08:45:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343677AbjLKNpl (ORCPT ); Mon, 11 Dec 2023 08:45:41 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 44C8BC3 for ; Mon, 11 Dec 2023 05:45:47 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60EA5C433C7; Mon, 11 Dec 2023 13:45:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1702302346; bh=Vimk7e5q40vbEzlVSqmm3kbcefcVNReNYU3xVrjn7UM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Ia8K5YU07aWkSia4+D7y7qWaRQSjVcDxDW60yyrWupGZojJs0MjFRSnA3lYB1ztL5 xT9BJBX3m2oTKskbvhVuyIMK9M3rtASK0Rcc3jDUyYVDBRNbY+zj6BtAsMru6dOTA+ 1f9+4NGo3LpW0314VlkPmTpmk1olfSMGJqC1TV3M3jaMG71JttQ9sqiSFR5ol0aCbI qbvbj4NixxpeOVD7KYX16ZnZTFVMrpZPgpTPviTB9rihySzYIFh+6xNxiPK959LASY gB+OZ3LWpa/naoR/t2GYzpe6vEU1mB75GKvx8YCseHHa293/fZrQUkKE4zGprZjUry 4bGhfYhRIis4Q== Date: Mon, 11 Dec 2023 15:45:42 +0200 From: Leon Romanovsky To: Daniel Vacek Cc: Jason Gunthorpe , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, Yuya Fujita-bishamonten Subject: Re: [PATCH 1/2] IB/ipoib: Fix mcast list locking Message-ID: <20231211134542.GG4870@unreal> References: <20231211130426.1500427-1-neelx@redhat.com> <20231211130426.1500427-2-neelx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231211130426.1500427-2-neelx@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 11, 2023 at 02:04:24PM +0100, Daniel Vacek wrote: > We need an additional protection against list removal between ipoib_mcast_join_task() > and ipoib_mcast_dev_flush() in case the &priv->lock needs to be dropped while > iterating the &priv->multicast_list in ipoib_mcast_join_task(). If the mcast > is removed while the lock was dropped, the for loop spins forever resulting > in a hard lockup (as was reported on RHEL 4.18.0-372.75.1.el8_6 kernel): > > Task A (kworker/u72:2 below) | Task B (kworker/u72:0 below) > -----------------------------------+----------------------------------- > ipoib_mcast_join_task(work) | ipoib_ib_dev_flush_light(work) > spin_lock_irq(&priv->lock) | __ipoib_ib_dev_flush(priv, ...) > list_for_each_entry(mcast, | ipoib_mcast_dev_flush(dev = priv->dev) > &priv->multicast_list, list) | mutex_lock(&priv->mcast_mutex) > ipoib_mcast_join(dev, mcast) | > spin_unlock_irq(&priv->lock) | > | spin_lock_irqsave(&priv->lock, flags) > | list_for_each_entry_safe(mcast, tmcast, > | &priv->multicast_list, list) > | list_del(&mcast->list); > | list_add_tail(&mcast->list, &remove_list) > | spin_unlock_irqrestore(&priv->lock, flags) > spin_lock_irq(&priv->lock) | > | ipoib_mcast_remove_list(&remove_list) > (Here, mcast is no longer on the | list_for_each_entry_safe(mcast, tmcast, > &priv->multicast_list and we keep | remove_list, list) > spinning on the &remove_list of the \ >>> wait_for_completion(&mcast->done) > other thread which is blocked and the| > list is still valid on it's stack.) | mutex_unlock(&priv->mcast_mutex) > > Fix this by adding mutex_lock(&priv->mcast_mutex) to ipoib_mcast_join_task(). I don't entirely understand the issue and the proposed solution. There is only one spin_unlock_irq() in the middle of list_for_each_entry(mcast, &priv->multicast_list, list) and it is right before return statement which will break the loop. So how will loop spin forever? Thanks > Unfortunately we could not reproduce the lockup and confirm this fix but > based on the code review I think this fix should address such lockups. > > crash> bc 31 > PID: 747 TASK: ff1c6a1a007e8000 CPU: 31 COMMAND: "kworker/u72:2" > -- > [exception RIP: ipoib_mcast_join_task+0x1b1] > RIP: ffffffffc0944ac1 RSP: ff646f199a8c7e00 RFLAGS: 00000002 > RAX: 0000000000000000 RBX: ff1c6a1a04dc82f8 RCX: 0000000000000000 > work (&priv->mcast_task{,.work}) > RDX: ff1c6a192d60ac68 RSI: 0000000000000286 RDI: ff1c6a1a04dc8000 > &mcast->list > RBP: ff646f199a8c7e90 R8: ff1c699980019420 R9: ff1c6a1920c9a000 > R10: ff646f199a8c7e00 R11: ff1c6a191a7d9800 R12: ff1c6a192d60ac00 > mcast > R13: ff1c6a1d82200000 R14: ff1c6a1a04dc8000 R15: ff1c6a1a04dc82d8 > dev priv (&priv->lock) &priv->multicast_list (aka head) > ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 > --- --- > #5 [ff646f199a8c7e00] ipoib_mcast_join_task+0x1b1 at ffffffffc0944ac1 [ib_ipoib] > #6 [ff646f199a8c7e98] process_one_work+0x1a7 at ffffffff9bf10967 > > crash> rx ff646f199a8c7e68 > ff646f199a8c7e68: ff1c6a1a04dc82f8 <<< work = &priv->mcast_task.work > > crash> list -hO ipoib_dev_priv.multicast_list ff1c6a1a04dc8000 > (empty) > > crash> ipoib_dev_priv.mcast_task.work.func,mcast_mutex.owner.counter ff1c6a1a04dc8000 > mcast_task.work.func = 0xffffffffc0944910 , > mcast_mutex.owner.counter = 0xff1c69998efec000 > > crash> b 8 > PID: 8 TASK: ff1c69998efec000 CPU: 33 COMMAND: "kworker/u72:0" > -- > #3 [ff646f1980153d50] wait_for_completion+0x96 at ffffffff9c7d7646 > #4 [ff646f1980153d90] ipoib_mcast_remove_list+0x56 at ffffffffc0944dc6 [ib_ipoib] > #5 [ff646f1980153de8] ipoib_mcast_dev_flush+0x1a7 at ffffffffc09455a7 [ib_ipoib] > #6 [ff646f1980153e58] __ipoib_ib_dev_flush+0x1a4 at ffffffffc09431a4 [ib_ipoib] > #7 [ff646f1980153e98] process_one_work+0x1a7 at ffffffff9bf10967 > > crash> rx ff646f1980153e68 > ff646f1980153e68: ff1c6a1a04dc83f0 <<< work = &priv->flush_light > > crash> ipoib_dev_priv.flush_light.func,broadcast ff1c6a1a04dc8000 > flush_light.func = 0xffffffffc0943820 , > broadcast = 0x0, > > The mcast(s) on the &remove_list (the remaining part of the ex &priv->multicast_list): > > crash> list -s ipoib_mcast.done.done ipoib_mcast.list -H ff646f1980153e10 | paste - - > ff1c6a192bd0c200 done.done = 0x0, > ff1c6a192d60ac00 done.done = 0x0, > > Reported-by: Yuya Fujita-bishamonten > Signed-off-by: Daniel Vacek > --- > drivers/infiniband/ulp/ipoib/ipoib_multicast.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c > index 5b3154503bf4..8e4f2c8839be 100644 > --- a/drivers/infiniband/ulp/ipoib/ipoib_multicast.c > +++ b/drivers/infiniband/ulp/ipoib/ipoib_multicast.c > @@ -580,6 +580,7 @@ void ipoib_mcast_join_task(struct work_struct *work) > } > netif_addr_unlock_bh(dev); > > + mutex_lock(&priv->mcast_mutex); > spin_lock_irq(&priv->lock); > if (!test_bit(IPOIB_FLAG_OPER_UP, &priv->flags)) > goto out; > @@ -634,6 +635,7 @@ void ipoib_mcast_join_task(struct work_struct *work) > /* Found the next unjoined group */ > if (ipoib_mcast_join(dev, mcast)) { > spin_unlock_irq(&priv->lock); > + mutex_unlock(&priv->mcast_mutex); > return; > } > } else if (!delay_until || > @@ -655,6 +657,7 @@ void ipoib_mcast_join_task(struct work_struct *work) > ipoib_mcast_join(dev, mcast); > > spin_unlock_irq(&priv->lock); > + mutex_unlock(&priv->mcast_mutex); > } > > void ipoib_mcast_start_thread(struct net_device *dev) > -- > 2.43.0 >