Re: zfs questions

["J. Hannken-Illjes" <hannken%mailbox.org@localhost>]

> On 1. Mar 2026, at 15:13, Takashi YAMAMOTO <yamt9999%gmail.com@localhost> wrote:
> 
> On Fri, Feb 20, 2026 at 5:09 PM Takashi YAMAMOTO <yamt9999%gmail.com@localhost> wrote:
>> 
>> hi,
>> 
>> recently i have used netbsd zfs and have a few questions.
>> 
>> * what's the purpose of zfs_zget_cleaner/VN_RELE_CLEANER?
>>  i have read the explanation in
>> https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=59885 .
>>  but i don't understand why we want to avoid the normal zfs_zget in
>> the first place.
>>  for me, it seems working w/o these special versions of functions:
>>  https://github.com/yamt/netbsd-src/commit/438ec29437465e0b7e2b831d4452159f83cad0cf
>>  (i will attach the same patch to this mail for those who don't like github.)
> 
> this version had a few deadlock issues.
> 
> i will attach a fixed version i'm currently testing.
> 
>> 
>> * is anyone using zfs in netbsd seriously? :-)
>> 
>> * does anyone have a plan to update the codebase to recent openzfs?
> <a.diff>

This patch makes the situation better but it fires assertions during unmount.

Running some stress tests on a 16-core amd64 vm with DEBUG+LOCKDEBUG and
kern.maxvnodes=1105 unmount crashes as it tries to load a vnode during unmount:


panic: kernel diagnostic assertion "mp == NULL || (mp->mnt_iflag & IMNT_UNMOUNT) == 0 || vp->v_tag == VT_VFS" failed: file "src/sys/kern/vfs_mount.c", line 545

#12  vfs_insmntque (vp=0xffffb751d4324a80, mp=0xffffb751cf2e2000) at src/sys/kern/vfs_mount.c:545
#13  vcache_get (mp=0xffffb751cf2e2000, key=key@entry=0xffffc3070a334bc8, key_len=key_len@entry=8, vpp=vpp@entry=0xffffc3070a334bd8) at src/sys/kern/vfs_vnode.c:1666
#14  zfs_zget (zfsvfs=zfsvfs@entry=0xffffc3002f7ba000, obj_num=<optimized out>, obj_num@entry=24865, zpp=zpp@entry=0xffffc3070a334c20) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_znode.c:1287
#15  zfs_get_data (arg=0xffffc3002f7ba000, lr=0xffffc30048cd41d8, buf=0xffffc30048cd4298 "", zio=0xffffb751e587e840) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vnops.c:1500
#16  zil_lwb_commit (zilog=<optimized out>, itx=0xffffb7517fb6f5c0, lwb=0xffffb751bffa25f8) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zil.c:1144
#17 zil_commit_writer (zilog=0xffffb751e664d540) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zil.c:1556
#18 zil_commit (zilog=0xffffb751e664d540, foid=<optimized out>) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zil.c:1638
#19  zil_commit (zilog=0xffffb751e664d540, foid=0) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zil.c:1620
#20 zil_close (zilog=0xffffb751e664d540) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zil.c:1856
#21  zfsvfs_teardown (zfsvfs=zfsvfs@entry=0xffffc3002f7ba000, unmounting=unmounting@entry=1) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vfsops.c:2288
#22  zfs_umount (vfsp=0xffffb751cf2e2000, fflag=524288) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vfsops.c:2445
#23  VFS_UNMOUNT (mp=mp@entry=0xffffb751cf2e2000, a=a@entry=524288) at src/sys/kern/vfs_subr.c:1526
#24  dounmount (mp=mp@entry=0xffffb751cf2e2000, flags=524288, l=l@entry=0xffffb751e855d800) at src/sys/kern/vfs_mount.c:980
#25  sys_unmount (l=0xffffb751e855d800, uap=0xffffc3070a335000, retval=<optimized out>) at src/sys/kern/vfs_syscalls.c:728
#26  sy_call (sy=0xffffffff8210a050 <sysent+528>, l=0xffffb751e855d800, uap=0xffffc3070a335000, rval=0xffffc3070a334fb0) at src/sys/sys/syscallvar.h:65
#27 sy_invoke (sy=0xffffffff8210a050 <sysent+528>, l=0xffffb751e855d800, uap=0xffffc3070a335000, rval=0xffffc3070a334fb0, code=22) at src/sys/sys/syscallvar.h:94
#28  syscall (frame=0xffffc3070a335000) at src/sys/arch/x86/x86/syscall.c:137
#29  handle_syscall ()

Here we have mp != NULL and mp->mnt_iflag == 0x122 (IMNT_MPSAFE | IMNT_NCLOOKUP | IMNT_UNMOUNT)


Disabling this assertion zfs unmount fails to destroy a list as it is not empty:


panic: solaris assert: list->list_head.list_next == node, file: src/sys/../external/cddl/osnet/dist/uts/common/os/list.c, line: 86

#12  list_destroy (list=list@entry=0xffff940059153040) at src/sys/../external/cddl/osnet/dist/uts/common/os/list.c:86
#13  zfsvfs_free (zfsvfs=0xffff940059152000) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vfsops.c:1439
#14  zfs_freevfs (vfsp=0xffff859a2e81d000) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vfsops.c:2782
#15 zfs_umount (vfsp=0xffff859a2e81d000, fflag=<optimized out>) at src/sys/../external/cddl/osnet/dist/uts/common/fs/zfs/zfs_vfsops.c:2471
#16  VFS_UNMOUNT (mp=mp@entry=0xffff859a2e81d000, a=a@entry=524288) at src/sys/kern/vfs_subr.c:1526
#17  dounmount (mp=mp@entry=0xffff859a2e81d000, flags=524288, l=l@entry=0xffff859a6a698400) at src/sys/kern/vfs_mount.c:980
#18  sys_unmount (l=0xffff859a6a698400, uap=0xffff94070afdc000, retval=<optimized out>) at src/sys/kern/vfs_syscalls.c:728
#19  sy_call (sy=0xffffffff8210a050 <sysent+528>, l=0xffff859a6a698400, uap=0xffff94070afdc000, rval=0xffff94070afdbfb0) at src/sys/sys/syscallvar.h:65
#20  sy_invoke (sy=0xffffffff8210a050 <sysent+528>, l=0xffff859a6a698400, uap=0xffff94070afdc000, rval=0xffff94070afdbfb0, code=22) at src/sys/sys/syscallvar.h:94
#21 syscall (frame=0xffff94070afdc000) at src/sys/arch/x86/x86/syscall.c:137
#22  handle_syscall ()

where *list is (list_t *) 0xffff940059153040:

{
  list_size = 240,
  list_offset = 200,
  list_head = {
    list_next = 0xffff859a07007ab8,
    list_prev = 0xffff8599c322bea8
  }
}

--
J. Hannken-Illjes - hannken%mailbox.org@localhost