ztest creates partially initialized root dataset

[loli10K]

Motivation and Context

Since d8fdfc2 was integrated dsl_pool_create() does not call dmu_objset_create_impl() for the root dataset when running in userland (ztest): this creates a pool with a partially initialized root dataset. Trying to import and use this pool results in both zpool and zfs executables dumping core.

root@linux:~# cat /proc/sys/kernel/spl/gitrev 
zfs-0.8.0-rc2-65-g6955b40
root@linux:~# ztest -p issue -T 10 -f /var/tmp/ -v 1 -s 128m -k 0 > /dev/null 2>&1
root@linux:~# echo $?
0
root@linux:~# zpool import -d /var/tmp/ issue
Aborted
root@linux:~# zfs list
Aborted
root@linux:~# ulimit -c unlimited 
root@linux:~# zfs list
Aborted (core dumped)
root@linux:~# gdb -q zfs core 
Reading symbols from zfs...done.
[New LWP 27733]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `zfs list'.
Program terminated with signal SIGABRT, Aborted.
#0  0x00007f01922c1067 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
56	../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  0x00007f01922c1067 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
#1  0x00007f01922c2448 in __GI_abort () at abort.c:89
#2  0x00007f01930a1ed6 in make_dataset_handle_common (zhp=0x253d480, zc=0x7ffc25c96ea0) at libzfs_dataset.c:450
#3  0x00007f01930a2075 in make_dataset_handle (hdl=0x2533060, path=0x2534d30 "issue") at libzfs_dataset.c:488
#4  0x00007f019309e024 in zfs_iter_root (hdl=0x2533060, func=0x405738 <zfs_callback>, data=0x7ffc25c9a4e0) at libzfs_config.c:449
#5  0x00000000004062db in zfs_for_each (argc=0, argv=0x2534cf0, flags=6, types=(ZFS_TYPE_FILESYSTEM | ZFS_TYPE_SNAPSHOT | ZFS_TYPE_VOLUME), sortcol=0x0, proplist=0x7ffc25c9a610, limit=0, callback=0x40c9ba <list_callback>, data=0x7ffc25c9a600) at zfs_iter.c:440
#6  0x000000000040cdbe in zfs_do_list (argc=0, argv=0x2534cf0) at zfs_main.c:3420
#7  0x00000000004163fa in main (argc=2, argv=0x7ffc25c9a788) at zfs_main.c:8042
(gdb) frame 2
#2  0x00007f01930a1ed6 in make_dataset_handle_common (zhp=0x253d480, zc=0x7ffc25c96ea0) at libzfs_dataset.c:450
450			abort();
(gdb) list
445		else if (zhp->zfs_dmustats.dds_type == DMU_OST_ZFS)
446			zhp->zfs_head_type = ZFS_TYPE_FILESYSTEM;
447		else if (zhp->zfs_dmustats.dds_type == DMU_OST_OTHER)
448			return (-1);
449		else
450			abort();
451	
452		if (zhp->zfs_dmustats.dds_is_snapshot)
453			zhp->zfs_type = ZFS_TYPE_SNAPSHOT;
454		else if (zhp->zfs_dmustats.dds_type == DMU_OST_ZVOL)
(gdb) p zhp->zfs_name 
$1 = "issue", '\000' <repeats 250 times>
(gdb) p zhp->zfs_dmustats.dds_type
$2 = DMU_OST_NONE
(gdb) 

This was discovered while testing #8181 (see buildbot ztest failures)

Description

Fix this by adopting an alternative change suggested in OpenZFS 8607 code review (https://www.illumos.org/rb/r/666/#comment2909).

How Has This Been Tested?

Run ztest, import "ztest" pool

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.

[codecov]

Codecov Report

Merging #8277 into master will increase coverage by 8.71%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8277      +/-   ##
==========================================
+ Coverage   68.24%   76.96%   +8.71%     
==========================================
  Files         335      369      +34     
  Lines      109770   114842    +5072     
==========================================
+ Hits        74917    88387   +13470     
+ Misses      34853    26455    -8398

Flag	Coverage Δ
#kernel	76.8% <100%> (+9.74%)	⬆️
#user	66.7% <100%> (+6.38%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6955b40...c65f730. Read the comment docs.

[behlendorf]

Thanks! I noticed this myself a little while back and was meaning to investigate.

[tcaputi]

LGTM. good catch.