Re: Arm v7 RPi2 -current unresponsive to debugger escape during buildworld

From: bob prohaska <fbsd_at_www.zefox.net>
Date: Tue, 25 Nov 2025 03:56:56 UTC 
On Mon, Nov 24, 2025 at 06:07:26PM -0800, bob prohaska wrote:
> A few minutes ago a Pi2 running buildworld for -current locked up again, with no
> responsie to the debugger escape.
> 
> The system was swapping fairly hard but not stuck, maybe 600 MB in use, eventually
> swap use declined but in minutes it got stuck with top displaying:
> 
> last pid: 51520;  load averages:    2.82,    2.96,    2.96                     up 1+02:48:27  16:27:58
> 57 processes:  3 running, 54 sleeping
> CPU: 66.4% user,  0.0% nice, 16.0% system,  0.3% interrupt, 17.4% idle
> Mem: 183M Active, 540M Inact, 416K Laundry, 175M Wired, 98M Buf, 19M Free
> Swap: 2048M Total, 23M Used, 2025M Free, 1% Inuse
> 
>   PID USERNAME    THR PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
> 51497 root          5  59    0   352M   208M uwait    3   0:08 161.51% ld.lld
> 51518 root          1 101    0   167M    71M CPU1     1   0:03  87.52% cc
> 51520 root          1  59    0   167M    72M RUN      2   0:03  67.88% cc
> 11811 root          1   0    0  6724K  1456K CPU0     0   5:51   0.46% top
>  2047 root          1   0    0  4676K   704K select   0   1:08   0.09% powerd
>  2206 bob           1   0    0    14M  1212K select   0   0:46   0.06% sshd-session
>  2119 root          1   9    0    14M  2320K select   1   1:27   0.00% sshd
> 
> The over-100% utilization for cpu 3 looks somewhat implausible. 
> Might it suggest anything significant? I haven't seen this from 
> top in a long time, so relatively speaking it's new behavior. 
> 
> There were no console warnings of any kind.

A few minutes after a restart of the -j3 buildworld that the machine had been working on
a spontaneous debugger excursion occurred:

dev = da0s2d, block = 47297583, fs = /usr
panic: ffs_blkfree_cg: freeing free frag
cpuid = 2
time = 1764039108
KDB: stack backtrace:
db_trace_self() at db_trace_self
         pc = 0xc0626ee4  lr = 0xc0076968 (db_trace_self_wrapper+0x30)
         sp = 0xc4eeda50  fp = 0xc4eedb68
db_trace_self_wrapper() at db_trace_self_wrapper+0x30
         pc = 0xc0076968  lr = 0xc0307a60 (vpanic+0x140)
         sp = 0xc4eedb70  fp = 0xc4eedb90
         r4 = 0x00000100  r5 = 0x00000000
         r6 = 0xc0775b24  r7 = 0xc0b7a8e4
vpanic() at vpanic+0x140
         pc = 0xc0307a60  lr = 0xc0307920 (vpanic)
         sp = 0xc4eedb98  fp = 0xc4eedb9c
         r4 = 0x00000000  r5 = 0xd76da900
         r6 = 0x00003a80  r7 = 0x00000007
         r8 = 0x00003a87  r9 = 0xc5f3a7d8
        r10 = 0xd76cd000
vpanic() at vpanic
         pc = 0xc0307920  lr = 0xc0586354 (ffs_blkfree_cg+0x7a8)
         sp = 0xc4eedba4  fp = 0xc4eedc28
         r4 = 0x00000007  r5 = 0x00003a87
         r6 = 0xc5f3a7d8  r7 = 0xd76cd000
         r8 = 0xc4eedb9c  r9 = 0xc0307920
        r10 = 0xc4eedba4
ffs_blkfree_cg() at ffs_blkfree_cg+0x7a8
         pc = 0xc0586354  lr = 0xc0581ce8 (ffs_blkfree+0x100)
         sp = 0xc4eedc30  fp = 0xc4eedc90
         r4 = 0x00001000  r5 = 0x00000004
         r6 = 0x00000000  r7 = 0x02d1b42f
         r8 = 0xc4eedce0  r9 = 0x0169436a
        r10 = 0x00000000
ffs_blkfree() at ffs_blkfree+0x100
         pc = 0xc0581ce8  lr = 0xc05b1cd0 (freework_freeblock+0x790)
         sp = 0xc4eedc98  fp = 0xc4eedd00
         r4 = 0x0169436a  r5 = 0xc4eedce0
         r6 = 0x00001000  r7 = 0x00000001
         r8 = 0xc078f34c  r9 = 0xdd44f3d0
        r10 = 0xd76da900
freework_freeblock() at freework_freeblock+0x790
         pc = 0xc05b1cd0  lr = 0xc05a30fc (handle_workitem_freeblocks+0x1f8)
         sp = 0xc4eedd08  fp = 0xc4eedd50
         r4 = 0xdd44f380  r5 = 0xd734d4c8
         r6 = 0xd76da900  r7 = 0xc07a28e4
         r8 = 0xd734d480  r9 = 0xd734d4c0
        r10 = 0xffffffff
handle_workitem_freeblocks() at handle_workitem_freeblocks+0x1f8
         pc = 0xc05a30fc  lr = 0xc059b79c (process_worklist_item+0x22c)
         sp = 0xc4eedd58  fp = 0xc4eedda0
         r4 = 0x00000004  r5 = 0xc078f34c
         r6 = 0xdd44f380  r7 = 0xd76da900
         r8 = 0xd76da900  r9 = 0xc4eedd60
        r10 = 0xffffffff
process_worklist_item() at process_worklist_item+0x22c
         pc = 0xc059b79c  lr = 0xc05963c8 (softdep_process_worklist+0xc4)
         sp = 0xc4eedda8  fp = 0xc4eeddd8
         r4 = 0x00000000  r5 = 0xc078f34c
         r6 = 0x0000000a  r7 = 0x00000028
         r8 = 0xd76da900  r9 = 0x00000000
        r10 = 0xc4ff6a80
softdep_process_worklist() at softdep_process_worklist+0xc4
         pc = 0xc05963c8  lr = 0xc0599f1c (softdep_flush+0x130)
         sp = 0xc4eedde0  fp = 0xc4eede18
         r4 = 0xc4ff6a80  r5 = 0x00000001
         r6 = 0x00200000  r7 = 0x00000000
         r8 = 0xc078f34c  r9 = 0xc4ff6a88
        r10 = 0xd76da900
softdep_flush() at softdep_flush+0x130
         pc = 0xc0599f1c  lr = 0xc02bb8cc (fork_exit+0xa0)
         sp = 0xc4eede20  fp = 0xc4eede38
         r4 = 0xc4eede40  r5 = 0xc4fa1800
         r6 = 0xc0599dec  r7 = 0xc4f74e40
         r8 = 0xc4ff6a80  r9 = 0xc0b8d184
        r10 = 0xc4f72c00
fork_exit() at fork_exit+0xa0
         pc = 0xc02bb8cc  lr = 0xc06296f4 (swi_exit)
         sp = 0xc4eede40  fp = 0x00000000
         r4 = 0xc0599dec  r5 = 0xc4ff6a80
         r6 = 0x7ff747b2  r7 = 0x00002710
         r8 = 0xc10051d0 r10 = 0xc4f72c00
swi_exit() at swi_exit
         pc = 0xc06296f4  lr = 0xc06296f4 (swi_exit)
         sp = 0xc4eede40  fp = 0x00000000
KDB: enter: panic
[ thread pid 18 tid 100086 ]
Stopped at      kdb_enter+0x54: ldrb    r15, [r15, r15, ror r15]!
db>  

The machine had been idling for a couple of hours, so it probably 
finished its background fsck before re-starting buildworld.

This is the first time in recent memory that buildworld has
ended in the debugger, if in fact builworld was the cause.


Thanks for reading,

bob prohaska