[PATCH 2/2] nvme-multipath: fix I/O stall when remapping namespaces
Hannes Reinecke
hare at suse.de
Wed Sep 4 01:20:19 PDT 2024
On 9/3/24 21:38, Sagi Grimberg wrote:
>
>
>
> On 03/09/2024 21:03, 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 how this helps given that you don't wait for srcu to synchronize
> before you kick the requeue.
>
It certainly is helping in my testcase. But having a synchronize_srcu
here is probably not a bad idea.
>> }
>> void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>
> Why do you need to clear NVME_NSHEAD_DISK_LIVE ? In the last posting you
> mentioned that ns_remove is stuck on srcu_synchronize? Can you explain
> why nvme_find_path is able to find a path given that it is already
> cleared NVME_NS_READY ? oris it nvme_available_path that is missing a
> check? Maybe can do with checking NVME_NS_READY instead?
Turned out that the reasoning in the previous revision wasn't quite
correct; since then I have seen several test-run where the above stack
trace was the _only_ one in the system, so the stall in removing
namespaces is more a side-effect. The ns_head was still visible
in sysfs while in that state, with exactly one path left:
# ls /sys/block
nvme0c4n1 nvme0c4n3 nvme0n1 nvme0n3 nvme0c4n2 nvme0c4n5 nvme0n2
nvme0n5
(whereas there had been 6 controllers with 6 namespaces).
So we fail to trigger a requeue to restart I/O on the stuck scanning
process; the actual path state really don't matter as never get this far.
This can happen when the partition scan triggered by device_add_disk()
(from one controller) interleaves with nvme_ns_remove() from another
controller. Both processes are running lockless wrt to ns_head at that
time, so if the partition scan issues I/O after the schedule_work
in nvme_mpath_shutdown_disk():
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)) {
nvme_cdev_del(&head->cdev, &head->cdev_device);
del_gendisk(head->disk);
}
}
_and_ that last path happens to be an 'inaccessible' one, I/O will be
requeued in the ns_head but never restarted, leaving to a hung process.
Note, that I/O might also be triggered by userspace (eg udev); the
device node is still present at that time. And that's also what I see
in my test runs; occasionally I get additional stuck udev processes:
[<0>] __folio_lock+0x114/0x1f0
[<0>] truncate_inode_pages_range+0x3c0/0x3e0
[<0>] blkdev_flush_mapping+0x45/0xe0
[<0>] blkdev_put_whole+0x2e/0x40
[<0>] bdev_release+0x129/0x1b0
[<0>] blkdev_release+0xd/0x20
[<0>] __fput+0xf7/0x2d0
also waiting on I/O.
You might be right checking for NS_READY might be sufficient, I'll be
checking. But we definitely need to requeue I/O after we called
del_gendisk().
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
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