[PATCH 2/2] nvme-multipath: fix I/O stall when remapping namespaces

[Hannes Reinecke]

On 9/4/24 16:52, Nilay Shroff wrote:
> 
> 
> On 9/3/24 23:33, Hannes Reinecke wrote:
>> During repetitive namespace remapping operations (ie removing a namespace and
>> provision a different namespace with the same NSID) on the target the
>> namespace might have changed between the time the initial scan
>> was performed, and partition scan was invoked by device_add_disk()
>> in nvme_mpath_set_live(). We then end up with a stuck scanning process:
>>
>> [<0>] folio_wait_bit_common+0x12a/0x310
>> [<0>] filemap_read_folio+0x97/0xd0
>> [<0>] do_read_cache_folio+0x108/0x390
>> [<0>] read_part_sector+0x31/0xa0
>> [<0>] read_lba+0xc5/0x160
>> [<0>] efi_partition+0xd9/0x8f0
>> [<0>] bdev_disk_changed+0x23d/0x6d0
>> [<0>] blkdev_get_whole+0x78/0xc0
>> [<0>] bdev_open+0x2c6/0x3b0
>> [<0>] bdev_file_open_by_dev+0xcb/0x120
>> [<0>] disk_scan_partitions+0x5d/0x100
>> [<0>] device_add_disk+0x402/0x420
>> [<0>] nvme_mpath_set_live+0x4f/0x1f0 [nvme_core]
>> [<0>] nvme_mpath_add_disk+0x107/0x120 [nvme_core]
>> [<0>] nvme_alloc_ns+0xac6/0xe60 [nvme_core]
>> [<0>] nvme_scan_ns+0x2dd/0x3e0 [nvme_core]
>> [<0>] nvme_scan_work+0x1a3/0x490 [nvme_core]
>>
>> This happens when we have several paths, some of which are inaccessible,
>> and the active paths are removed first. Then nvme_find_path() will requeue
>> I/O in the ns_head (as paths are present), but the requeue list is never
>> triggered as all remaining paths are inactive.
>> This patch checks for NVME_NSHEAD_DISK_LIVE when selecting a path,
>> and requeue I/O after NVME_NSHEAD_DISK_LIVE has been cleared once
>> the last path has been removed to properly terminate pending I/O.
>>
>> Signed-off-by: Hannes Reinecke <hare at kernel.org>
>> ---
>>   drivers/nvme/host/multipath.c | 14 ++++++++++++--
>>   1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
>> index c9d23b1b8efc..1b1deb0450ab 100644
>> --- a/drivers/nvme/host/multipath.c
>> +++ b/drivers/nvme/host/multipath.c
>> @@ -407,6 +407,9 @@ static struct nvme_ns *nvme_numa_path(struct nvme_ns_head *head)
>>   
>>   inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
>>   {
>> +	if (!test_bit(NVME_NSHEAD_DISK_LIVE, &head->flags))
>> +		return NULL;
>> +
>>   	switch (READ_ONCE(head->subsys->iopolicy)) {
>>   	case NVME_IOPOLICY_QD:
>>   		return nvme_queue_depth_path(head);
>> @@ -421,6 +424,9 @@ static bool nvme_available_path(struct nvme_ns_head *head)
>>   {
>>   	struct nvme_ns *ns;
>>   
>> +	if (!test_bit(NVME_NSHEAD_DISK_LIVE, &head->flags))
>> +		return NULL;
>> +
>>   	list_for_each_entry_rcu(ns, &head->list, siblings) {
>>   		if (test_bit(NVME_CTRL_FAILFAST_EXPIRED, &ns->ctrl->flags))
>>   			continue;
>> @@ -967,11 +973,15 @@ void nvme_mpath_shutdown_disk(struct nvme_ns_head *head)
>>   {
>>   	if (!head->disk)
>>   		return;
>> -	kblockd_schedule_work(&head->requeue_work);
>> -	if (test_bit(NVME_NSHEAD_DISK_LIVE, &head->flags)) {
>> +	if (test_and_clear_bit(NVME_NSHEAD_DISK_LIVE, &head->flags)) {
>>   		nvme_cdev_del(&head->cdev, &head->cdev_device);
>>   		del_gendisk(head->disk);
>>   	}
>> +	/*
>> +	 * requeue I/O after NVME_NSHEAD_DISK_LIVE has been cleared
>> +	 * to allow multipath to fail all I/O.
>> +	 */
>> +	kblockd_schedule_work(&head->requeue_work);
>>   }
> Not sure, in your case, whether nvme_mpath_remove_disk() is called or not?
> The nvme_mpath_remove_disk() shall trigger the ns_head reqiest list.
> 
It would, but we're never get this far as the reference to ns_head it 
held by the above stack trace (and nvme_mpath_remove_disk()) is called
when the last reference to ns_head drops.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare at suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich