Re: zfs questions

[Takashi YAMAMOTO <yamt9999%gmail.com@localhost>]

hi,

On Tue, Mar 3, 2026 at 10:22 PM J. Hannken-Illjes <hannken%mailbox.org@localhost> wrote:
>
> > On 2. Mar 2026, at 17:16, Takashi YAMAMOTO <yamt9999%gmail.com@localhost> wrote:
> >
> > hi,
> >
> > On Mon, Mar 2, 2026 at 8:19 PM J. Hannken-Illjes <hannken%mailbox.org@localhost> wrote:
> >>
> >>> 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)
> >
> > it's an interesting crash. thank you.
> > i tried to reproduce it by myself. but no luck.
> > the attached patch (b.diff) would fix it.
>
> Running vflush() until all vnodes are flushed works.  I used the attached and functinal equivalent diff and
> my load tests ran for 6 hours without problem.

thank you.

>
> Allowing to attach new vnodes until the mount is IMNT_GONE looks ok.
>
> Not sure we need to assert TAILQ_EMPTY(&mp->mnt_vnodelist), the "dangling vnode" panic below should catch it.

ok.

>
> > well, honestly speaking, i don't understand why zil_close commits the
> > zil in the first place.
> > my impression is that it should not be necessary because we are
> > syncing txg for unmount anyway.
> > what do you think?
>
> No idea -- its been much too long I looked deeper int ZFS internals.

who's our zfs maintainer these days?

>
> >> 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
> > <b.diff>
>
> --
> J. Hannken-Illjes - hannken%mailbox.org@localhost
>