Comment 18 for bug 1839521

Verification done for linux on xenial-proposed.

The inodes for file, xattr dir, and xattr child are all evicted at file removal time, not making it to any disposal list after file removal.

So the window/scenario for the problem to occur is not present anymore.

Log
---

$ uname -rv
4.4.0-160-generic #188-Ubuntu SMP Wed Aug 14 04:21:43 UTC 2019

$ modinfo zfs | head
filename: /lib/modules/4.4.0-160-generic/kernel/zfs/zfs/zfs.ko
version: 0.6.5.6-0ubuntu28
...
srcversion: 99F1D0FED2F291CA7AED0C6

$ sudo apt-get install zfsutils-linux attr

$ sudo ./zfs-mount.sh

$ echo 2 | sudo tee /proc/sys/vm/drop_caches
2

$ sudo ./zfs-kprobes.sh

$ sudo cat /sys/kernel/debug/tracing/trace_pipe &

$ touch /zfs/file
           touch-10656 [001] d... 359.615887: p_zfs_mknode_0: (zfs_mknode+0x0/0xe00 [zfs]) flag=0x0 dzp=0xffff8800b9875940
           touch-10656 [001] d... 359.616184: p_zfs_znode_alloc_0: (zfs_znode_alloc+0x0/0x520 [zfs]) obj=0xa
           touch-10656 [001] d... 359.616339: r_zfs_znode_alloc_0: (zfs_mknode+0x8a3/0xe00 [zfs] <- zfs_znode_alloc) zpp=0xffff880036f48440

$ setfattr -n user.debug -v 1 /zfs/file
        setfattr-10657 [000] d... 361.507063: p_zfs_mknode_0: (zfs_mknode+0x0/0xe00 [zfs]) flag=0x2 dzp=0xffff880036f48440
        setfattr-10657 [000] d... 361.507265: p_zfs_znode_alloc_0: (zfs_znode_alloc+0x0/0x520 [zfs]) obj=0xb
        setfattr-10657 [000] d... 361.507402: r_zfs_znode_alloc_0: (zfs_mknode+0x8a3/0xe00 [zfs] <- zfs_znode_alloc) zpp=0xffff880139d09980
        setfattr-10657 [000] d... 361.507665: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xa
        setfattr-10657 [000] d... 361.507792: r_zfs_zget_0: (zfs_zaccess+0x12b/0x220 [zfs] <- zfs_zget)
        setfattr-10657 [000] d... 361.507981: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xa
        setfattr-10657 [000] d... 361.508104: r_zfs_zget_0: (zfs_zaccess+0x12b/0x220 [zfs] <- zfs_zget)
        setfattr-10657 [000] d... 361.508692: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xa
        setfattr-10657 [000] d... 361.508821: r_zfs_zget_0: (zfs_zaccess+0x12b/0x220 [zfs] <- zfs_zget)
        setfattr-10657 [000] d... 361.509022: p_zfs_mknode_0: (zfs_mknode+0x0/0xe00 [zfs]) flag=0x0 dzp=0xffff880139d09980
        setfattr-10657 [000] d... 361.509170: p_zfs_znode_alloc_0: (zfs_znode_alloc+0x0/0x520 [zfs]) obj=0xc
        setfattr-10657 [000] d... 361.509302: r_zfs_znode_alloc_0: (zfs_mknode+0x8a3/0xe00 [zfs] <- zfs_znode_alloc) zpp=0xffff880139d09100

$ rm /zfs/file
              rm-10658 [001] d... 363.216716: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xa
              rm-10658 [001] d... 363.216882: r_zfs_zget_0: (zfs_dirent_lock+0x56c/0x6c0 [zfs] <- zfs_zget)
              rm-10658 [001] d... 363.217130: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xb
              rm-10658 [001] d... 363.217271: r_zfs_zget_0: (zfs_remove+0x22b/0x4c0 [zfs] <- zfs_zget)
              rm-10658 [001] d... 363.217567: p_zpl_evict_inode_0: (zpl_evict_inode+0x0/0x60 [zfs]) inode=0xffff880036f48650
              rm-10658 [001] d... 363.217715: p_zfs_inactive_0: (zfs_inactive+0x0/0x270 [zfs]) inode=0xffff880036f48650
              rm-10658 [001] d... 363.217835: p_zfs_zinactive_0: (zfs_zinactive+0x0/0xe0 [zfs]) znode=0xffff880036f48440 obj=0xa
              rm-10658 [001] d... 363.217963: p_zfs_rmnode_0: (zfs_rmnode+0x0/0x360 [zfs]) znode=0xffff880036f48440
              rm-10658 [001] d... 363.218102: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xb
              rm-10658 [001] d... 363.218232: r_zfs_zget_0: (zfs_rmnode+0x25b/0x360 [zfs] <- zfs_zget)
              rm-10658 [001] d... 363.218464: p_zfs_iput_async_0: (zfs_iput_async+0x0/0x60 [zfs]) inode=0xffff880139d09b90 obj=0x0
           <...>-10308 [003] d... 363.218496: p_zpl_evict_inode_0: (zpl_evict_inode+0x0/0x60 [zfs]) inode=0xffff880139d09b90
          z_iput-10308 [003] d... 363.218503: p_zfs_inactive_0: (zfs_inactive+0x0/0x270 [zfs]) inode=0xffff880139d09b90
          z_iput-10308 [003] d... 363.218505: p_zfs_zinactive_0: (zfs_zinactive+0x0/0xe0 [zfs]) znode=0xffff880139d09980 obj=0xb
          z_iput-10308 [003] d... 363.218509: p_zfs_rmnode_0: (zfs_rmnode+0x0/0x360 [zfs]) znode=0xffff880139d09980
          z_iput-10308 [003] d... 363.218512: p_zfs_purgedir_0: (zfs_purgedir+0x0/0x230 [zfs]) znode=0xffff880139d09980
          z_iput-10308 [003] d... 363.218560: p_zfs_zget_0: (zfs_zget+0x0/0x230 [zfs]) zsb=0xffff8800bb12c000 obj=0xc
          z_iput-10308 [003] d... 363.218566: r_zfs_zget_0: (zfs_purgedir+0xb4/0x230 [zfs] <- zfs_zget)
          z_iput-10308 [003] d... 363.218606: p_zfs_iput_async_0: (zfs_iput_async+0x0/0x60 [zfs]) inode=0xffff880139d09310 obj=0x0
          z_iput-10308 [003] d... 363.218626: r_zfs_purgedir_0: (zfs_rmnode+0x272/0x360 [zfs] <- zfs_purgedir)
          z_iput-10308 [003] d... 363.218663: p_zpl_evict_inode_0: (zpl_evict_inode+0x0/0x60 [zfs]) inode=0xffff880139d09310
          z_iput-10308 [003] d... 363.218665: p_zfs_inactive_0: (zfs_inactive+0x0/0x270 [zfs]) inode=0xffff880139d09310
          z_iput-10308 [003] d... 363.218665: p_zfs_zinactive_0: (zfs_zinactive+0x0/0xe0 [zfs]) znode=0xffff880139d09100 obj=0xc
          z_iput-10308 [003] d... 363.218667: p_zfs_rmnode_0: (zfs_rmnode+0x0/0x360 [zfs]) znode=0xffff880139d09100

$ echo 2 | sudo tee /proc/sys/vm/drop_caches
2
           <...>-10661 [003] d... 372.513411: p_dispose_list_0: (dispose_list+0x0/0x50)
             tee-10661 [003] d... 372.513525: p_dispose_list_0: (dispose_list+0x0/0x50)
             tee-10661 [003] d... 372.513836: p_dispose_list_0: (dispose_list+0x0/0x50)
             tee-10661 [003] d... 372.514065: p_dispose_list_0: (dispose_list+0x0/0x50)
             tee-10661 [003] d... 372.516630: p_dispose_list_0: (dispose_list+0x0/0x50)
             tee-10661 [003] d... 372.516691: p_dispose_list_0: (dispose_list+0x0/0x50)
             tee-10661 [003] d... 372.516830: p_dispose_list_0: (dispose_list+0x0/0x50)