[RFC] nvmet: Always remove processed AER elements from list

[Daniel Wagner]

All async events are enqueued via nvmet_add_async_event() which
updates the ctrl->async_event_cmds[] array and additionally an struct
nvmet_async_event is added to the ctrl->async_events list.

Under normal operations the nvmet_async_event_work() updates again the
ctrl->async_event_cmds and removes the corresponding struct
nvmet_async_event from the list again. Though nvmet_sq_destroy() could
be called which calles nvmet_async_events_free() which only updates
the ctrl->async_event_cmds[] array.

Add a new function nvmet_async_events_process() which processes the
async events and updates both array and the list. With this we avoid
having two places where the array and list are modified.

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Signed-off-by: Daniel Wagner <dwagner@xxxxxxx>
---
Hi,

I've got following oops:

PID: 79413  TASK: ffff92f03a814ec0  CPU: 19  COMMAND: "kworker/19:2"
#0 [ffffa5308b8c3c58] machine_kexec at ffffffff8e05dd02
#1 [ffffa5308b8c3ca8] __crash_kexec at ffffffff8e12102a
#2 [ffffa5308b8c3d68] crash_kexec at ffffffff8e122019
#3 [ffffa5308b8c3d80] oops_end at ffffffff8e02e091
#4 [ffffa5308b8c3da0] general_protection at ffffffff8e8015c5
    [exception RIP: nvmet_async_event_work+94]
    RIP: ffffffffc0d9a80e  RSP: ffffa5308b8c3e58  RFLAGS: 00010202
    RAX: dead000000000100  RBX: ffff92dcbc7464b0  RCX: 0000000000000002
    RDX: 0000000000040002  RSI: 38ffff92dc9814cf  RDI: ffff92f217722f20
    RBP: ffff92dcbc746418   R8: 0000000000000000   R9: 0000000000000000
    R10: 000000000000035b  R11: ffff92efb8dd2091  R12: ffff92dcbc7464a0
    R13: ffff92dbe03a5f29  R14: 0000000000000000  R15: 0ffff92f92f26864
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
#5 [ffffa5308b8c3e78] process_one_work at ffffffff8e0a3b0c
#6 [ffffa5308b8c3eb8] worker_thread at ffffffff8e0a41e7
#7 [ffffa5308b8c3f10] kthread at ffffffff8e0a93af
#8 [ffffa5308b8c3f50] ret_from_fork at ffffffff8e800235

this maps to nvmet_async_event_results. So it looks like this function
access a stale aen pointer:

static u32 nvmet_async_event_result(struct nvmet_async_event *aen)
{
        return aen->event_type | (aen->event_info << 8) | (aen->log_page << 16);
}

The test which is executed removes during operation one of the nodes.

The only odd thing I could figure out so far is that the list is not
updated in sync with the array in all cases. I suppose this could be
the source of the crash. Not verified yet.

Johannes though it makes sense to post this as question.

Thanks,
Daniel

 drivers/nvme/target/core.c | 39 +++++++++++++++++----------------------
 1 file changed, 17 insertions(+), 22 deletions(-)

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 3a67e244e568..9d9efd585847 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -129,27 +129,8 @@ static u32 nvmet_async_event_result(struct nvmet_async_event *aen)
 	return aen->event_type | (aen->event_info << 8) | (aen->log_page << 16);
 }
 
-static void nvmet_async_events_free(struct nvmet_ctrl *ctrl)
+static void nvmet_async_events_process(struct nvmet_ctrl *ctrl, u16 status)
 {
-	struct nvmet_req *req;
-
-	while (1) {
-		mutex_lock(&ctrl->lock);
-		if (!ctrl->nr_async_event_cmds) {
-			mutex_unlock(&ctrl->lock);
-			return;
-		}
-
-		req = ctrl->async_event_cmds[--ctrl->nr_async_event_cmds];
-		mutex_unlock(&ctrl->lock);
-		nvmet_req_complete(req, NVME_SC_INTERNAL | NVME_SC_DNR);
-	}
-}
-
-static void nvmet_async_event_work(struct work_struct *work)
-{
-	struct nvmet_ctrl *ctrl =
-		container_of(work, struct nvmet_ctrl, async_event_work);
 	struct nvmet_async_event *aen;
 	struct nvmet_req *req;
 
@@ -163,16 +144,30 @@ static void nvmet_async_event_work(struct work_struct *work)
 		}
 
 		req = ctrl->async_event_cmds[--ctrl->nr_async_event_cmds];
-		nvmet_set_result(req, nvmet_async_event_result(aen));
+		if (status == 0)
+			nvmet_set_result(req, nvmet_async_event_result(aen));
 
 		list_del(&aen->entry);
 		kfree(aen);
 
 		mutex_unlock(&ctrl->lock);
-		nvmet_req_complete(req, 0);
+		nvmet_req_complete(req, status);
 	}
 }
 
+static void nvmet_async_events_free(struct nvmet_ctrl *ctrl)
+{
+	nvmet_async_events_process(ctrl, NVME_SC_INTERNAL | NVME_SC_DNR);
+}
+
+static void nvmet_async_event_work(struct work_struct *work)
+{
+	struct nvmet_ctrl *ctrl =
+		container_of(work, struct nvmet_ctrl, async_event_work);
+
+	nvmet_async_events_process(ctrl, 0);
+}
+
 void nvmet_add_async_event(struct nvmet_ctrl *ctrl, u8 event_type,
 		u8 event_info, u8 log_page)
 {
-- 
2.16.4