From mboxrd@z Thu Jan 1 00:00:00 1970 From: jonathan.derrick@intel.com (Jon Derrick) Date: Thu, 18 Jun 2015 09:59:32 -0600 Subject: [PATCH] NVMe: Fixed race between nvme_thread & probe path. In-Reply-To: <1434624230-25050-1-git-send-email-Parav.pandit@avagotech.com> References: <1434624230-25050-1-git-send-email-Parav.pandit@avagotech.com> Message-ID: <20150618155932.GA1276@localhost.localdomain> On Thu, Jun 18, 2015@04:13:50PM +0530, Parav Pandit wrote: > Kernel thread nvme_thread and driver load process can be executing > in parallel on different CPU. This leads to race condition whenever > nvme_alloc_queue() instructions are executed out of order that can > reflects incorrect value for nvme_thread. > Memory barrier in nvme_alloc_queue() ensures that it maintains the > order and and data dependency read barrier in reader thread ensures > that cpu cache is synced. > > Signed-off-by: Parav Pandit > --- > drivers/block/nvme-core.c | 12 ++++++++++-- > 1 files changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c > index 5961ed7..90fb0ce 100644 > --- a/drivers/block/nvme-core.c > +++ b/drivers/block/nvme-core.c > @@ -1403,8 +1403,10 @@ static struct nvme_queue *nvme_alloc_queue(struct nvme_dev *dev, int qid, > nvmeq->q_db = &dev->dbs[qid * 2 * dev->db_stride]; > nvmeq->q_depth = depth; > nvmeq->qid = qid; > - dev->queue_count++; > dev->queues[qid] = nvmeq; > + /* update queues first before updating queue_count */ > + smp_wmb(); > + dev->queue_count++; > > return nvmeq; > This has been applied already as an explicit mb() > @@ -2073,7 +2075,13 @@ static int nvme_kthread(void *data) > continue; > } > for (i = 0; i < dev->queue_count; i++) { > - struct nvme_queue *nvmeq = dev->queues[i]; > + struct nvme_queue *nvmeq; > + > + /* make sure to read queue_count before > + * traversing queues. > + */ > + smp_read_barrier_depends(); > + nvmeq = dev->queues[i]; > if (!nvmeq) > continue; > spin_lock_irq(&nvmeq->q_lock); I don't think this is necessary. If queue_count is incremented while in this loop, it will be picked up the next time the kthread runs