Re: zfs questions

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

i committed the patch with a few more fixes, including sync=always handling.

On Wed, Mar 4, 2026 at 9:42 PM Takashi YAMAMOTO <yamt9999%gmail.com@localhost> wrote:
>
> 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
> >