Messages in this thread Patch in this message | | | Date | Wed, 29 Nov 2023 17:24:07 +0800 | From | yaoma <> | Subject | Re: [PATCH] nvme: fix deadlock between reset and scan |
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Hi, Sagi Grimberg
I revised my code following your advice and carried out tests.
Test Scripts: for ((t=1;t<=128;t++)) do nsid=`nvme create-ns /dev/nvme0 -s 1453772 -c 1453772 -f 0\ -m 0 -d 0 | awk -F: '{print($NF);}'` nvme attach-ns /dev/nvme0 -n $nsid -c 0 done
echo "resetting" nvme reset /dev/nvme0 lsblk | grep nvme0 | wc -l sleep 2 lsblk | grep nvme0 | wc -l
Results: ... attach-ns: Success, nsid:128 resetting 23 128
After the fix, we will not be deadlocked.
I find a minor issue. In the resetting state, the scan may not recognize all ns, but since a scan work is queued at the end of reset, so the impact is not significant. After the reset is completed, all ns can eventually be recognized.
--- diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index 21783aa2e..e361aba39 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -3630,6 +3630,10 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info) goto out_unlink_ns;
down_write(&ctrl->namespaces_rwsem); + if (test_bit(NVME_CTRL_FROZEN, &ctrl->flags)) { + up_write(&ctrl->namespaces_rwsem); + goto out_unlink_ns; + } nvme_ns_add_to_ctrl_list(ns); up_write(&ctrl->namespaces_rwsem); nvme_get_ctrl(ctrl); @@ -4539,6 +4543,7 @@ void nvme_unfreeze(struct nvme_ctrl *ctrl) list_for_each_entry(ns, &ctrl->namespaces, list) blk_mq_unfreeze_queue(ns->queue); up_read(&ctrl->namespaces_rwsem); + clear_bit(NVME_CTRL_FROZEN, &ctrl->flags); } EXPORT_SYMBOL_GPL(nvme_unfreeze);
@@ -4572,6 +4577,7 @@ void nvme_start_freeze(struct nvme_ctrl *ctrl) { struct nvme_ns *ns;
+ set_bit(NVME_CTRL_FROZEN, &ctrl->flags); down_read(&ctrl->namespaces_rwsem); list_for_each_entry(ns, &ctrl->namespaces, list) blk_freeze_queue_start(ns->queue); diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index f35647c47..755319b0d 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -251,6 +251,7 @@ enum nvme_ctrl_flags { NVME_CTRL_STOPPED = 3, NVME_CTRL_SKIP_ID_CNS_CS = 4, NVME_CTRL_DIRTY_CAPABILITY = 5, + NVME_CTRL_FROZEN = 6, };
struct nvme_ctrl { -- On 2023/11/28 18:13, Sagi Grimberg wrote: > > > On 11/28/23 08:22, yaoma wrote: >> Hi Keith Busch >> >> Thanks for your reply. >> >> The idea to avoid such a deadlock between nvme_reset and nvme_scan is >> to ensure that no namespace can be added to ctrl->namespaces after >> nvme_start_freeze has already been called. We can achieve this goal by >> assessing the ctrl->state after we have already acquired the >> ctrl->namespaces_rwsem lock, to decide whether to add the namespace to >> the list or not. >> 1. After we determine that ctrl->state is LIVE, it may be immediately >> changed to another state. However, since we have already acquired the >> lock, other tasks cannot access ctrl->namespace, so we can still >> safely add the namespace to the list. After acquiring the lock, >> nvme_start_freeze will freeze all ns->q in the list, including any >> newly added namespaces. >> 2. Before the completion of nvme_reset, ctrl->state will not be >> changed to LIVE, so we will not add any more namespaces to the list. >> All ns->q in the list is frozen, so nvme_wait_freeze can exit normally. > > I agree with the analysis, there is a hole between start_freeze and > freeze_wait that a scan may add a ns to the ctrl ns list. > > However the fix should be to mark the ctrl with say NVME_CTRL_FROZEN > flag set in nvme_freeze_start and cleared in nvme_unfreeze (similar > to what we did with quiesce). Then the scan can check it before adding > the new namespace (under the namespaces_rwsem).
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