Re: BUG() in 2.4: sg direct IO + exit()

[Douglas Gilbert <dougg@torque.net>]

Tony Battersby wrote:
> The following BUG() is triggered in 2.4.x when a program calls exit()
> immediately after sending a SCSI command that uses direct IO:
> 
> kernel BUG at page_alloc.c:98!
> invalid operand: 0000
> sg sym53c8xx_2 e1000
> CPU:    0
> EIP:    0010:[<c0133d22>]    Not tainted
> EFLAGS: 00010202
> EIP is at __free_pages_ok+0x32/0x2b0 [kernel]
> eax: 00000001   ebx: c12aceb0   ecx: c12aceb0   edx: 00000000
> esi: 00000000   edi: 00000000   ebp: 00000001   esp: c02bbe94
> ds: 0018   es: 0018   ss: 0018
> Process swapper (pid: 0, stackpage=c02bb000)
> Stack: cfefc640 cfdf2de8 cfbe93c0 cfefc600 00000001 00000000 cfefc600
> c12aceb0
>        cf926fa0 00000000 cfb8b040 c0127cb0 cfb8b04c cfb8b04c cfb8b000
> d0885db6
>        cf926fa0 00000000 cfb8b040 d0885cc9 cfb8b04c 00000001 cfd08680
> cfd086c8
> Call Trace:
>  [<c0127cb0>] unmap_kiobuf+0x30/0x50 [kernel]
>  [<d0885db6>] sg_unmap_and+0x26/0x50 [sg]
>  [<d0885cc9>] sg_finish_rem_req+0x39/0x70 [sg]
>  [<d0885451>] sg_cmd_done_bh+0x281/0x380 [sg]
>  [<c01ab65a>] scsi_finish_command+0xda/0xe0 [kernel]
>  [<c01ab380>] scsi_bottom_half_handler+0xc0/0x230 [kernel]
>  [<c011dacb>] bh_action+0x4b/0x90 [kernel]
>  [<c011d971>] tasklet_hi_action+0x61/0xa0 [kernel]
>  [<c011d6fb>] do_softirq+0x6b/0xd0 [kernel]
>  [<c0108baf>] do_IRQ+0xdf/0xf0 [kernel]
>  [<c01052c0>] default_idle+0x0/0x40 [kernel]
>  [<c01052c0>] default_idle+0x0/0x40 [kernel]
>  [<c010b388>] call_do_IRQ+0x5/0xd [kernel]
>  [<c01052c0>] default_idle+0x0/0x40 [kernel]
>  [<c01052c0>] default_idle+0x0/0x40 [kernel]
>  [<c01052ec>] default_idle+0x2c/0x40 [kernel]
>  [<c0105372>] cpu_idle+0x52/0x70 [kernel]
>  [<c0105000>] stext+0x0/0x50 [kernel]
> 
> Code: 0f 0b 62 00 ab 04 23 c0 89 d8 e8 2f ed ff ff 8b 7b 28 85 ff
>  <0>Kernel panic: Aiee, killing interrupt handler!
> In interrupt handler - not syncing
> 
> The following program reproduces the problem:
> 
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> #include <unistd.h>
> #include <scsi/sg.h>
> #include <limits.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> 
> unsigned char mode_sense_cdb[] = { 0x1a, 0x00, 0x3f, 0x00, 0xff, 0x00 };
> 
> int main(int argc, char *argv[])
> {
>     int fd;
>     unsigned char sense_data[256];
>     unsigned char buf[256];
>     sg_io_hdr_t io;
> 
>     fd = open("/dev/sg0", O_RDWR);
>     if (fd == -1) {
>         perror("open(/dev/sg0)");
>         exit(1);
>     }
> 
>     memset(&io, 0, sizeof(sg_io_hdr_t));
>     io.interface_id = 'S';
>     io.timeout = UINT_MAX;
>     io.flags = SG_FLAG_DIRECT_IO;
>     io.sbp = sense_data;
>     io.mx_sb_len = 0xff;
>     io.cmdp = mode_sense_cdb;
>     io.cmd_len = 6;
>     io.dxfer_direction = SG_DXFER_FROM_DEV;
>     io.dxferp = buf;
>     io.dxfer_len = 0xff;
>     write(fd, &io, sizeof(sg_io_hdr_t));
> 
>     return 0;
> }
> 
> Just compile, echo 1 > /proc/scsi/sg/allow_dio, and run.  The SCSI
> device that I am using is a tape drive, but it shouldn't matter.
> 
> I have tested this with 2.4.21+kksymoops and 2.4.26-pre5+kksymoops with
> the same results.  The above stack trace is from 2.4.26-pre5.  I haven't
> tried 2.6.
> 
> I am running a SMP kernel on a UP Intel P4 with 256 MB RAM.  The test
> machine does not have any swap space configured (swapoff -a).

Tony,
It is not causing an oops when I try with scsi_debug and lk 2.6.5-rc2.
Neither is there a problem with a Suse 9 stock SMP kernel
(2.4.21-99-smp4G) on an old dual celeron (A-bit mb) box with a
Sony SDT-7000 tape drive on /dev/sg0.

I'll keep looking. The oops suggests that the memory is not being
locked down (as you are probably aware).

Doug Gilbert