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16 Sep 2019 12:07:26 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan3.iad.amazon.com [10.40.159.166]) by email-inbound-relay-1d-9ec21598.us-east-1.amazon.com (Postfix) with ESMTPS id 1FCFFA20B4; Mon, 16 Sep 2019 12:07:25 +0000 (UTC) Received: from EX13D01UWB001.ant.amazon.com (10.43.161.75) by EX13MTAUWB001.ant.amazon.com (10.43.161.207) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 16 Sep 2019 12:07:25 +0000 Received: from EX13D01UWB002.ant.amazon.com (10.43.161.136) by EX13d01UWB001.ant.amazon.com (10.43.161.75) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 16 Sep 2019 12:07:24 +0000 Received: from EX13D01UWB002.ant.amazon.com ([10.43.161.136]) by EX13d01UWB002.ant.amazon.com ([10.43.161.136]) with mapi id 15.00.1367.000; Mon, 16 Sep 2019 12:07:24 +0000 From: "Singh, Balbir" To: "hch@lst.de" , "sblbir@amzn.com" Subject: Re: [PATCH v2 1/2] nvme/host/pci: Fix a race in controller removal Thread-Topic: [PATCH v2 1/2] nvme/host/pci: Fix a race in controller removal Thread-Index: AQHVaowXMhT5fp4jR0Gn8rYSgg/tw6ct8YgAgABH9gA= Date: Mon, 16 Sep 2019 12:07:24 +0000 Message-ID: <336bb49fae2a723bdd31cad1ffe10110a0efb6ee.camel@amazon.com> References: <20190913233631.15352-1-sblbir@amzn.com> <20190916074948.GB25606@lst.de> In-Reply-To: <20190916074948.GB25606@lst.de> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.43.161.217] Content-ID: <0C566049C544D84AB27DDB81B4D13DCA@amazon.com> MIME-Version: 1.0 Precedence: Bulk X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190916_050729_218493_4D948F5B X-CRM114-Status: GOOD ( 28.37 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "kbusch@kernel.org" , "axboe@fb.com" , "sagi@grimberg.me" , "linux-nvme@lists.infradead.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Mon, 2019-09-16 at 09:49 +0200, Christoph Hellwig wrote: > On Fri, Sep 13, 2019 at 11:36:30PM +0000, Balbir Singh wrote: > > This race is hard to hit in general, now that we > > have the shutdown_lock in both nvme_reset_work() and > > nvme_dev_disable() > > > > The real issue is that after doing all the setup work > > in nvme_reset_work(), when get another timeout (nvme_timeout()), > > then we proceed to disable the controller. This causes > > the reset work to only partially progress and then fail. > > > > Depending on the progress made, we call into > > nvme_remove_dead_ctrl(), which does another > > nvme_dev_disable() freezing the block-mq queues. > > > > I've noticed a race with udevd with udevd trying to re-read > > the partition table, it ends up with the bd_mutex held and > > it ends up waiting in blk_queue_enter(), since we froze > > the queues in nvme_dev_disable(). nvme_kill_queues() calls > > revalidate_disk() and ends up waiting on the bd_mutex > > resulting in a deadlock. > > > > Allow the hung tasks a chance by unfreezing the queues after > > setting dying bits on the queue, then call revalidate_disk() > > to update the disk size. > > > > NOTE: I've seen this race when the controller does not > > respond to IOs or abort requests, but responds to other > > commands and even signals it's ready after its reset, > > but still drops IO. I've tested this by emulating the > > behaviour in the driver. > > > > Signed-off-by: Balbir Singh > > --- > > > > Changelog: > > - Rely on blk_set_queue_dying to do the wake_all() > > > > drivers/nvme/host/core.c | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c > > index b45f82d58be8..f6ddb58a7013 100644 > > --- a/drivers/nvme/host/core.c > > +++ b/drivers/nvme/host/core.c > > @@ -103,10 +103,16 @@ static void nvme_set_queue_dying(struct > > nvme_ns *ns) > > */ > > if (!ns->disk || test_and_set_bit(NVME_NS_DEAD, &ns->flags)) > > return; > > - revalidate_disk(ns->disk); > > blk_set_queue_dying(ns->queue); > > /* Forcibly unquiesce queues to avoid blocking dispatch */ > > blk_mq_unquiesce_queue(ns->queue); > > + /* > > + * revalidate_disk, after all pending IO is cleaned up > > + * by blk_set_queue_dying, largely any races with blk parittion > > + * reads that might come in after freezing the queues, > > otherwise > > + * we'll end up waiting up on bd_mutex, creating a deadlock. > > + */ > > + revalidate_disk(ns->disk); > > The patch looks fine to me, but the comments looks a little strange. > How do we trigger the partition scan? Is someone opening the device > again after we froze it? The race itself is between the timeout for an aborted IO (iod->aborted = 1) causing a reset and the subsequent disable controller, eventually leading to IO errors on the device. To reproduce the issue I run fio on the block device, when due to timeout fio gets errors, it closes the device (/dev/nvme1), which triggers udevd to reread the partitions. But independent of this scenario, the race can be triggered by anything scanning or reading the partition at the time of reset/disable controller. Balbir Singh. _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme