Re: NULL pointer deref in ptcread()

On Tue, Apr 05, 2005 at 10:43:44AM -0700, Kris Kennaway wrote:
> HEAD from yesterday on a SMP machine.
> 
> Kris

FYI (well, slightly different panic), this was caused by resizing the
xterm that connected via ssh to screen running on this machine:

panic: clist reservation botch
cpuid = 1
KDB: enter: panic
[thread pid 720 tid 100222 ]
Stopped at      kdb_enter+0x30: leave
db> wh
Tracing pid 720 tid 100222 td 0xc5c0e170
kdb_enter(c06fa3a6,1,c06ff6b5,f7d31b30,c5c0e170) at kdb_enter+0x30
panic(c06ff6b5,c8951778,8,0,0) at panic+0x13e
b_to_q(f7d31b8c,7,c5864838,3f,f7d31b88) at b_to_q+0xd3
ttwrite(c5864800,f7d31c68,4,f7d31c40,c04e2fdd) at ttwrite+0x4a7
ptswrite(c5cfb600,f7d31c68,4,557,c5cfb600) at ptswrite+0x38
devfs_write_f(c5bb4438,f7d31c68,c5d2a200,0,c5c0e170) at devfs_write_f+0xc7
dofilewrite(c5c0e170,c5bb4438,3,809f000,100) at dofilewrite+0xb6
write(c5c0e170,f7d31d14,3a6,c0715405,c5c0e170) at write+0x6a
syscall(2f,2f,bfbf002f,0,100) at syscall+0x2c4
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (4, FreeBSD ELF32, write), eip = 0x2816fbb7, esp = 0xbfbfe3ec, ebp = 0xbfbfe408 ---

Process 720 is screen.  Looks like there's a race condition here.

Kris

> Fatal trap 12: page fault while in kernel mode
> cpuid = 1; apic id = 06
> fault virtual address   = 0x0
> fault code              = supervisor read, page not present
> instruction pointer     = 0x8:0xc06b4b02
> stack pointer           = 0x10:0xf7cb6b4c
> frame pointer           = 0x10:0xf7cb6b78
> code segment            = base 0x0, limit 0xfffff, type 0x1b
>                         = DPL 0, pres 1, def32 1, gran 1
> processor eflags        = interrupt enabled, resume, IOPL = 0
> current process         = 1182 (screen)
> [thread pid 1182 tid 100239 ]
> Stopped at      generic_bcopy+0x1a:     repe movsl      (%esi),%es:(%edi)
> db> wh
> Tracing pid 1182 tid 100239 td 0xc5a92b80
> generic_bcopy(c59aa438,f7cb6bb8,40,c0758280,1) at generic_bcopy+0x1a
> ptcread(c69b3d00,f7cb6c68,4,3ae,1000) at ptcread+0x180
> devfs_read_f(c5d8e558,f7cb6c68,c605e100,0,c5a92b80) at devfs_read_f+0xa7
> dofileread(c5a92b80,c5d8e558,7,bfbfd3f0,1000) at dofileread+0xc3
> read(c5a92b80,f7cb6d14,3a6,c0715022,c5a92b80) at read+0x6c
> syscall(2f,2f,bfbf002f,80aa050,0) at syscall+0x2c4
> Xint0x80_syscall() at Xint0x80_syscall+0x1f
> --- syscall (3, FreeBSD ELF32, read), eip = 0x2816fbd7, esp = 0xbfbfd3cc, ebp = 0xbfbfe408 ---
> db>