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Date:      Wed, 2 Mar 2016 01:12:31 -0800
From:      Maxim Sobolev <sobomax@FreeBSD.org>
To:        stable@freebsd.org, freebsd-fs@freebsd.org
Cc:        Kirk McKusick <mckusick@mckusick.com>, kib@freebsd.org
Subject:   Process stuck in "vnread"
Message-ID:  <CAH7qZfs3EwT8jnKyodHxF_5nK18MeLSaB_F-qqOfwV0MJMD7Vg@mail.gmail.com>

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Hi, I've encountered cp(1) process stuck in the vnread state on one of my
build machines that got recently upgraded to 10.3.

   0 79596     1   0  20  0   17092    1396 wait     I     1       0:00.00
/bin/sh /usr/local/bin/autoreconf -f -i
   0 79602 79596   0  52  0   41488    9036 wait     I     1       0:00.07
/usr/local/bin/perl -w /usr/local/bin/autoreconf-2.69 -f -i
   0 79639 79602   0  72  0       0       0 -        Z     1       0:00.27
<defunct>
   0 79762 79602   0  20  0   17092    1396 wait     I     1       0:00.00
/bin/sh /usr/local/bin/automake --add-missing --copy --force-missing
   0 79768 79762   0  52  0   49736   13936 wait     I     1       0:00.11
/usr/local/bin/perl -w /usr/local/bin/automake-1.15 --add-missing --copy
--force-missing
   0 79962 79768   0  20  0   12368    1024 vnread   DL    1       0:00.00
cp /usr/local/share/automake-1.15/compile ./compile

I am not sure if it's related to that OS version upgrade, but I have not
seen any such issues on the same machine in 2-3 years running essentially
the same build process with version 9.x, 10.0, 10.1 and 10.2.

$ uname -a
FreeBSD van01.sippysoft.com 10.3-PRERELEASE FreeBSD 10.3-PRERELEASE #1
80de3e2(master)-dirty: Tue Feb  2 12:19:57 PST 2016
sobomax@abc.sippysoft.com:/usr/obj/usr/home/sobomax/projects/freebsd103/sys/ABC
 amd64

The kernel stack trace is:

(kgdb) thread 360
[Switching to thread 360 (Thread 100515)]#0  0xffffffff8095244e in
sched_switch ()
(kgdb) bt
#0  0xffffffff8095244e in sched_switch ()
#1  0xffffffff809313b1 in mi_switch ()
#2  0xffffffff8097089a in sleepq_wait ()
#3  0xffffffff80930dd7 in _sleep ()
#4  0xffffffff809b230e in bwait ()
#5  0xffffffff80b511f3 in vnode_pager_generic_getpages ()
#6  0xffffffff80dd1607 in VOP_GETPAGES_APV ()
#7  0xffffffff80b4f59a in vnode_pager_getpages ()
#8  0xffffffff80b30031 in vm_fault_hold ()
#9  0xffffffff80b2f797 in vm_fault ()
#10 0xffffffff80cb5a75 in trap_pfault ()
#11 0xffffffff80cb51dd in trap ()
#12 0xffffffff80c9b122 in calltrap ()
#13 0xffffffff80cb36f1 in copyin ()
#14 0xffffffff80977ddf in uiomove_faultflag ()

The FS stack configuration is somewhat unique, so I am not sure if I am
hitting some rare race condition or lock ordering issues specific to that.
It's basically ZFS (ZRAID) on top of pair or SATA SSDs with big file on
that FS attached via md(4) and UFS2 on that md(4). The build itself runs in
chroot with that UFS2 fs as its primary root.

Just maybe additional bit of info, attempting to list the directory with
that UFS image also got my bash process stuck in "zfs" state, backtrace
from that is:

(kgdb) thread 353
[Switching to thread 353 (Thread 100508)]#0  0xffffffff8095244e in
sched_switch ()
(kgdb) bt
#0  0xffffffff8095244e in sched_switch ()
#1  0xffffffff809313b1 in mi_switch ()
#2  0xffffffff8097089a in sleepq_wait ()
#3  0xffffffff809069ad in sleeplk ()
#4  0xffffffff809060e0 in __lockmgr_args ()
#5  0xffffffff809b8b7c in vop_stdlock ()
#6  0xffffffff80dd0a3b in VOP_LOCK1_APV ()
#7  0xffffffff809d6d23 in _vn_lock ()
#8  0xffffffff81a8c9cd in ?? ()
#9  0x0000000000000000 in ?? ()



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