Bug 207621

This bug affect boards with Allwinner A20 chips. Once they have attached SATA SSD disk (no necessary to mount, only plugged in), then you will have troubles with reading more files from SD card.
I did small experiment - download last image (same experience with previous one), boot, and without any modifications start reading files from SD. Attached sata ssd have no UFS/FAT partition and no any partition is mounted. (my hardware is Banana PI M1)

Here is three examples:
read disk using tar with transfer data to another process (wc) and without (to dev/null)

Outputs from my experiment follows.

(Other affected people: 
https://lists.freebsd.org/pipermail/freebsd-arm/2016-February/013229.html
https://lists.freebsd.org/pipermail/freebsd-arm/2016-February/013274.html )

Jindra

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SATA disk attached, but not used:
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root@a20:~ # uname -a

FreeBSD a20 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r295683: Wed Feb 17 05:22:46 UTC 2016 root@releng2.nyi.freebsd.org:/usr/obj/arm.armv6/usr/src/sys/A20  arm
root@a20:~ # tar cf - /usr | wc

tar: Removing leading '/' from member names
panic: vm_page_insert_after: page already inserted
cpuid = 0
KDB: enter: panic
[ thread pid 679 tid 100084 ]
Stopped at      $d.7:   ldrb    r15, [r15, r15, ror r15]!
db>

---------------------------------------------
root@a20:~ # tar cf /dev/null /usr

tar: Removing leading '/' from member names
panic: vm_page_insert_after: page already inserted
cpuid = 0
KDB: enter: panic
[ thread pid 644 tid 100067 ]
Stopped at      $d.7:   ldrb    r15, [r15, r15, ror r15]!
db>


---------------------------------------------
NO SATA disk attached:
---------------------------------------------

root@a20:~ # uname -a

FreeBSD a20 11.0-CURRENT FreeBSD 11.0-CURRENT #0 r295683: Wed Feb 17 05:22:46 UTC 2016 root@releng2.nyi.freebsd.org:/usr/obj/arm.armv6/usr/src/sys/A20  arm
root@a20:~ # tar cf - /usr | wc

tar: Removing leading '/' from member names
 5994501 28169833 716206080
root@a20:~ #
root@a20:~ # halt

Feb 17 05:37:21 a20 halt: halted by root

Feb 17 05:37:21 a20 syslogd: exiting on signal 15

Waiting (max 60 seconds) for system process `vnlru' to stop...done
Waiting (max 60 seconds) for system process `bufdaemon' to stop...done
Waiting (max 60 seconds) for system process `syncer' to stop...
Syncing disks, vnodes remaining...2 1 0 0 done
All buffers synced.
lock order reversal:
 1st 0xc45b3db4 ufs (ufs) @ /usr/src/sys/kern/vfs_mount.c:1222
 2nd 0xc432cc94 syncer (syncer) @ /usr/src/sys/kern/vfs_subr.c:2617
stack backtrace:
lock order reversal:
 1st 0xc45b3b74 ufs (ufs) @ /usr/src/sys/kern/vfs_mount.c:1222
 2nd 0xc45b35d4 devfs (devfs) @ /usr/src/sys/fs/msdosfs/msdosfs_vfsops.c:994
stack backtrace:
Uptime: 3m12s

The operating system has halted.
Please press any key to reboot.