kern/39402: "panic: getblk: block size invariant failed" with fss

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

>Number:         39402
>Category:       kern
>Synopsis:       "panic: getblk: block size invariant failed" with fss
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Aug 24 18:55:00 +0000 2008
>Originator:     Manuel Bouyer
>Release:        NetBSD 4.99.72
>Organization:
>Environment:
System: NetBSD comore.lip6.fr 4.99.72 NetBSD 4.99.72 (XEN3_DOMU) #99: Sun Aug 
24 17:27:03 CEST 2008  
bouyer@rock:/dsk/l1/misc/bouyer/tmp/amd64/obj/dsk/l1/misc/bouyer/current/src/sys/arch/amd64/compile/XEN3_DOMU
 amd64
Architecture: amd64
Machine: amd64
>Description:
        running dump -X on a small filesystem leads to:
/mnt: suspended 0.070 sec, redo 1 of 4
panic: getblk: block size invariant failed
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip ffffffff8036f5f5 cs e030 rflags 246 cr2  7f7ffda14000 
cpl 0 rsp ffffa000043f5770
Stopped in pid 0.28 (system) at netbsd:breakpoint+0x5:  leave
breakpoint() at netbsd:breakpoint+0x5
panic() at netbsd:panic+0x255
getblk() at netbsd:getblk+0x19e
bio_doread() at netbsd:bio_doread+0x24
breadn() at netbsd:breadn+0x3c
ffs_snapshot_read() at netbsd:ffs_snapshot_read+0x136
ffs_read() at netbsd:ffs_read+0x97
VOP_READ() at netbsd:VOP_READ+0x2d
vn_rdwr() at netbsd:vn_rdwr+0xc6
fss_bs_io() at netbsd:fss_bs_io+0x9b
fss_bs_thread() at netbsd:fss_bs_thread+0x53a

        Note that /mnt is mounted -o log, and is otherwise empty
        (just newfs'd), and has no activity.
        After reboot, we have in /mnt:
comore:/home/bouyer>ll /mnt/
total 272
-rw-------  1 root  wheel  104857672 Aug 24 20:35 00000317aa
comore:/home/bouyer>df -h /mnt/
Filesystem        Size       Used      Avail %Cap Mounted on
/dev/xbd1a         97M       1.1M        91M   1% /mnt
After removing /mnt/00000317aa:
comore:/home/bouyer#df -h /mnt
Filesystem        Size       Used      Avail %Cap Mounted on
/dev/xbd1a         97M       1.0M        91M   1% /mnt

After some trial I found it happens on:
/dev/rxbd1a: 190.0MB (389120 sectors) block size 8192, fragment size 1024
        using 5 cylinder groups of 38.00MB, 4864 blks, 9472 inodes.
super-block backups (for fsck_ffs -b #) at:
32, 77856, 155680, 233504, 311328,

but not on:
/dev/rxbd1a: 200.0MB (409600 sectors) block size 8192, fragment size 1024
        using 5 cylinder groups of 40.00MB, 5120 blks, 9920 inodes.
super-block backups (for fsck_ffs -b #) at:
32, 81952, 163872, 245792, 327712,


>How-To-Repeat:
        boot a DIAGNOSTIC kernel
        create a partition of less than 190M
        newfs it
        mount -o log it
        dump -X the mount point
>Fix: