On Thu, Jun 20, 2024 at 09:51:46AM -0400, Benjamin Coddington wrote:
> On 19 Jun 2024, at 13:39, cel@xxxxxxxxxx wrote:
>
> > From: Chuck Lever <chuck.lever@xxxxxxxxxx>
> >
> > During generic/069 runs with pNFS SCSI layouts, the NFS client emits
> > the following in the system journal:
> >
> > kernel: pNFS: failed to open device /dev/disk/by-id/dm-uuid-mpath-0x6001405e3366f045b7949eb8e4540b51 (-2)
> > kernel: pNFS: using block device sdb (reservation key 0x666b60901e7b26b3)
> > kernel: pNFS: failed to open device /dev/disk/by-id/dm-uuid-mpath-0x6001405e3366f045b7949eb8e4540b51 (-2)
> > kernel: pNFS: using block device sdb (reservation key 0x666b60901e7b26b3)
> > kernel: sd 6:0:0:1: reservation conflict
> > kernel: sd 6:0:0:1: [sdb] tag#16 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> > kernel: sd 6:0:0:1: [sdb] tag#16 CDB: Write(10) 2a 00 00 00 00 50 00 00 08 00
> > kernel: reservation conflict error, dev sdb, sector 80 op 0x1:(WRITE) flags 0x0 phys_seg 1 prio class 2
> > kernel: sd 6:0:0:1: reservation conflict
> > kernel: sd 6:0:0:1: reservation conflict
> > kernel: sd 6:0:0:1: [sdb] tag#18 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> > kernel: sd 6:0:0:1: [sdb] tag#17 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> > kernel: sd 6:0:0:1: [sdb] tag#18 CDB: Write(10) 2a 00 00 00 00 60 00 00 08 00
> > kernel: sd 6:0:0:1: [sdb] tag#17 CDB: Write(10) 2a 00 00 00 00 58 00 00 08 00
> > kernel: reservation conflict error, dev sdb, sector 96 op 0x1:(WRITE) flags 0x0 phys_seg 1 prio class 0
> > kernel: reservation conflict error, dev sdb, sector 88 op 0x1:(WRITE) flags 0x0 phys_seg 1 prio class 0
> > systemd[1]: fstests-generic-069.scope: Deactivated successfully.
> > systemd[1]: fstests-generic-069.scope: Consumed 5.092s CPU time.
> > systemd[1]: media-test.mount: Deactivated successfully.
> > systemd[1]: media-scratch.mount: Deactivated successfully.
> > kernel: sd 6:0:0:1: reservation conflict
> > kernel: failed to unregister PR key.
> >
> > This appears to be due to a race. bl_alloc_lseg() calls this:
> >
> > 561 static struct nfs4_deviceid_node *
> > 562 bl_find_get_deviceid(struct nfs_server *server,
> > 563 const struct nfs4_deviceid *id, const struct cred *cred,
> > 564 gfp_t gfp_mask)
> > 565 {
> > 566 struct nfs4_deviceid_node *node;
> > 567 unsigned long start, end;
> > 568
> > 569 retry:
> > 570 node = nfs4_find_get_deviceid(server, id, cred, gfp_mask);
> > 571 if (!node)
> > 572 return ERR_PTR(-ENODEV);
> >
> > nfs4_find_get_deviceid() does a lookup without the spin lock first.
> > If it can't find a matching deviceid, it creates a new device_info
> > (which calls bl_alloc_deviceid_node, and that registers the device's
> > PR key).
> >
> > Then it takes the nfs4_deviceid_lock and looks up the deviceid again.
> > If it finds it this time, bl_find_get_deviceid() frees the spare
> > (new) device_info, which unregisters the PR key for the same device.
> >
> > Any subsequent I/O from this client on that device gets EBADE.
> >
> > The umount later unregisters the device's PR key again.
> >
> > To prevent this problem, register the PR key after the deviceid_node
> > lookup.
>
> Hi Chuck - nice catch, but I'm not seeing how we don't have the same problem
> after this patch, instead it just seems like it moves the race. What
> prevents another process waiting to take the nfs4_deviceid_lock from
> unregistering the same device? I think we need another way to signal
> bl_free_device that we don't want to unregister for the case where the new
> device isn't added to nfs4_deviceid_cache.
That's a (related but) somewhat different issue. I haven't seen
that in practice so far.
> No good ideas yet - maybe we can use a flag set within the
> nfs4_deviceid_lock?
Well this smells like a use for a reference count on the block
device, but fs/nfs doesn't control the definition of that data
structure.
> Ben
>
> >
> > Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> > ---
> > fs/nfs/blocklayout/blocklayout.c | 9 ++++++++-
> > fs/nfs/blocklayout/blocklayout.h | 1 +
> > fs/nfs/blocklayout/dev.c | 29 +++++++++++++++++++++--------
> > 3 files changed, 30 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
> > index 6be13e0ec170..75cc5e50bd37 100644
> > --- a/fs/nfs/blocklayout/blocklayout.c
> > +++ b/fs/nfs/blocklayout/blocklayout.c
> > @@ -571,8 +571,14 @@ bl_find_get_deviceid(struct nfs_server *server,
> > if (!node)
> > return ERR_PTR(-ENODEV);
> >
> > - if (test_bit(NFS_DEVICEID_UNAVAILABLE, &node->flags) == 0)
> > + if (test_bit(NFS_DEVICEID_UNAVAILABLE, &node->flags) == 0) {
> > + struct pnfs_block_dev *d =
> > + container_of(node, struct pnfs_block_dev, node);
> > + if (d->pr_reg)
> > + if (d->pr_reg(d) < 0)
> > + goto out_put;
> > return node;
> > + }
> >
> > end = jiffies;
> > start = end - PNFS_DEVICE_RETRY_TIMEOUT;
> > @@ -581,6 +587,7 @@ bl_find_get_deviceid(struct nfs_server *server,
> > goto retry;
> > }
> >
> > +out_put:
> > nfs4_put_deviceid_node(node);
> > return ERR_PTR(-ENODEV);
> > }
> > diff --git a/fs/nfs/blocklayout/blocklayout.h b/fs/nfs/blocklayout/blocklayout.h
> > index f1eeb4914199..8aabaf5218b8 100644
> > --- a/fs/nfs/blocklayout/blocklayout.h
> > +++ b/fs/nfs/blocklayout/blocklayout.h
> > @@ -116,6 +116,7 @@ struct pnfs_block_dev {
> >
> > bool (*map)(struct pnfs_block_dev *dev, u64 offset,
> > struct pnfs_block_dev_map *map);
> > + int (*pr_reg)(struct pnfs_block_dev *dev);
> > };
> >
> > /* sector_t fields are all in 512-byte sectors */
> > diff --git a/fs/nfs/blocklayout/dev.c b/fs/nfs/blocklayout/dev.c
> > index 356bc967fb5d..3d2401820ef4 100644
> > --- a/fs/nfs/blocklayout/dev.c
> > +++ b/fs/nfs/blocklayout/dev.c
> > @@ -230,6 +230,26 @@ static bool bl_map_stripe(struct pnfs_block_dev *dev, u64 offset,
> > return true;
> > }
> >
> > +static int bl_register_scsi(struct pnfs_block_dev *d)
> > +{
> > + struct block_device *bdev = file_bdev(d->bdev_file);
> > + const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
> > + int error;
> > +
> > + if (d->pr_registered)
> > + return 0;
> > +
> > + error = ops->pr_register(bdev, 0, d->pr_key, true);
> > + if (error) {
> > + trace_bl_pr_key_reg_err(bdev->bd_disk->disk_name, d->pr_key, error);
> > + return -error;
> > + }
> > +
> > + trace_bl_pr_key_reg(bdev->bd_disk->disk_name, d->pr_key);
> > + d->pr_registered = true;
> > + return 0;
> > +}
> > +
> > static int
> > bl_parse_deviceid(struct nfs_server *server, struct pnfs_block_dev *d,
> > struct pnfs_block_volume *volumes, int idx, gfp_t gfp_mask);
> > @@ -373,14 +393,7 @@ bl_parse_scsi(struct nfs_server *server, struct pnfs_block_dev *d,
> > goto out_blkdev_put;
> > }
> >
> > - error = ops->pr_register(bdev, 0, d->pr_key, true);
> > - if (error) {
> > - trace_bl_pr_key_reg_err(bdev->bd_disk->disk_name, d->pr_key, error);
> > - goto out_blkdev_put;
> > - }
> > - trace_bl_pr_key_reg(bdev->bd_disk->disk_name, d->pr_key);
> > -
> > - d->pr_registered = true;
> > + d->pr_reg = bl_register_scsi;
> > return 0;
> >
> > out_blkdev_put:
> > --
> > 2.45.1
>
--
Chuck Lever
