Re: USB audio w/ "D" state

[Albert D. Cahalan]

> I did "cat /bin/sh >> /dev/audio" and hit ^C to stop the noise.
> The "cat" process gets stuck in "D" state with the WCHAN indicating
> that the process is stuck 1/3 the way through the usbout_stop()
> function.
> 
> hardware:  Mac Cube and the normal spherical speakers (OHCI USB)
> kernel:    plain 2.4.16 from www.kernel.org
> compiler:  gcc version 2.95.4 20011006 (Debian prerelease)
> 
> In case PPC assembly is useful to somebody, I've marked the instruction
> where the process gets stuck. The surrounding "bl" instructions look
> like infinite loops to me, but maybe I'm reading this wrong. The assembly
> is from:   objdump -dl --start-address=0x1728 audio.o

I added --reloc to that. Since I had to copy by hand, I put the
branch targets on the right. I marked the WCHAN with '*' chars.
For those not used to PowerPC, "bl foo" is a function call to foo().

So here is a bit of the assembly:

    1790:       38 60 00 01     li      r3,1
    1794:       48 00 00 01     bl      schedule_timeout
*** 1798: ***** 7f a3 eb 78 *** mr **** r3,r29 ****************
    179c:       48 00 00 01     bl      __save_flags_ptr
    17a0:       48 00 00 01     bl      __cli

...and here is the C code for that:

schedule_timeout(1);
spin_lock_irqsave(&as->lock, flags);

The full disassembly:

usbout_stop():
    1728:       94 21 ff d0     stwu    r1,-48(r1)
    172c:       7c 08 02 a6     mflr    r0
    1730:       7d 80 00 26     mfcr    r12
    1734:       bf 81 00 20     stmw    r28,32(r1)
    1738:       90 01 00 34     stw     r0,52(r1)
    173c:       91 81 00 1c     stw     r12,28(r1)
    1740:       3b e3 03 98     addi    r31,r3,920
    1744:       3b c0 00 01     li      r30,1
    1748:       3b a1 00 08     addi    r29,r1,8
    174c:       7f a3 eb 78     mr      r3,r29
    1750:       48 00 00 01     bl      __save_flags_ptr
    1754:       48 00 00 01     bl      __cli
    1758:       83 9f 00 24     lwz     r28,36(r31)
    175c:       57 80 07 34     rlwinm  r0,r28,0,28,26
    1760:       90 1f 00 24     stw     r0,36(r31)
    1764:       80 61 00 08     lwz     r3,8(r1)
    1768:       48 00 00 01     bl      __restore_flags
    176c:       73 80 00 0f     andi.   r0,r28,15
    1770:       41 82 00 98     beq     1808 <usbout_stop+0xe0>
    1774:       31 3e ff ff     addic   r9,r30,-1
    1778:       7d 29 49 10     subfe   r9,r9,r9
    177c:       38 09 00 01     addi    r0,r9,1
    1780:       55 29 07 bc     rlwinm  r9,r9,0,30,30
    1784:       2e 1e 00 00     cmpwi   cr4,r30,0
    1788:       7d 29 03 78     or      r9,r9,r0
    178c:       91 22 00 00     stw     r9,0(r2)
    1790:       38 60 00 01     li      r3,1
    1794:       48 00 00 01     bl      schedule_timeout
*** 1798: ***** 7f a3 eb 78 *** mr **** r3,r29 ****************
    179c:       48 00 00 01     bl      __save_flags_ptr
    17a0:       48 00 00 01     bl      __cli
    17a4:       83 9f 00 24     lwz     r28,36(r31)
    17a8:       80 61 00 08     lwz     r3,8(r1)
    17ac:       48 00 00 01     bl      __restore_flags
    17b0:       41 92 ff bc     beq     cr4,176c <usbout_stop+0x44>
    17b4:       80 02 00 08     lwz     r0,8(r2)
    17b8:       2c 00 00 00     cmpwi   r0,0
    17bc:       41 82 ff b0     beq     176c <usbout_stop+0x44>
    17c0:       73 80 00 01     andi.   r0,r28,1
    17c4:       41 82 00 0c     beq     17d0 <usbout_stop+0xa8>
    17c8:       38 7f 00 28     addi    r3,r31,40
    17cc:       48 00 00 01     bl      usb_unlink_urb
    17d0:       73 80 00 02     andi.   r0,r28,2
    17d4:       41 82 00 0c     beq     17e0 <usbout_stop+0xb8>
    17d8:       38 7f 00 cc     addi    r3,r31,204
    17dc:       48 00 00 01     bl      usb_unlink_urb
    17e0:       73 80 00 04     andi.   r0,r28,4
    17e4:       41 82 00 0c     beq     17f0 <usbout_stop+0xc8>
    17e8:       38 7f 01 70     addi    r3,r31,368
    17ec:       48 00 00 01     bl      usb_unlink_urb
    17f0:       73 80 00 08     andi.   r0,r28,8
    17f4:       41 82 00 0c     beq     1800 <usbout_stop+0xd8>
    17f8:       38 7f 02 14     addi    r3,r31,532
    17fc:       48 00 00 01     bl      usb_unlink_urb
    1800:       3b c0 00 00     li      r30,0
    1804:       4b ff ff 68     b       176c <usbout_stop+0x44>
    1808:       3b a0 00 00     li      r29,0
    180c:       93 a2 00 00     stw     r29,0(r2)
    1810:       80 7f 00 4c     lwz     r3,76(r31)
    1814:       2c 03 00 00     cmpwi   r3,0
    1818:       41 82 00 08     beq     1820 <usbout_stop+0xf8>
    181c:       48 00 00 01     bl      kfree
    1820:       80 7f 00 f0     lwz     r3,240(r31)
    1824:       2c 03 00 00     cmpwi   r3,0
    1828:       41 82 00 08     beq     1830 <usbout_stop+0x108>
    182c:       48 00 00 01     bl      kfree
    1830:       80 7f 01 94     lwz     r3,404(r31)
    1834:       2c 03 00 00     cmpwi   r3,0
    1838:       41 82 00 08     beq     1840 <usbout_stop+0x118>
    183c:       48 00 00 01     bl      kfree
    1840:       80 7f 02 38     lwz     r3,568(r31)
    1844:       2c 03 00 00     cmpwi   r3,0
    1848:       41 82 00 08     beq     1850 <usbout_stop+0x128>
    184c:       48 00 00 01     bl      kfree
    1850:       93 bf 00 4c     stw     r29,76(r31)
    1854:       93 bf 02 38     stw     r29,568(r31)
    1858:       93 bf 01 94     stw     r29,404(r31)
    185c:       93 bf 00 f0     stw     r29,240(r31)
    1860:       80 01 00 34     lwz     r0,52(r1)
    1864:       81 81 00 1c     lwz     r12,28(r1)
    1868:       7c 08 03 a6     mtlr    r0
    186c:       bb 81 00 20     lmw     r28,32(r1)
    1870:       7d 80 81 20     mtcrf   8,r12
    1874:       38 21 00 30     addi    r1,r1,48
    1878:       4e 80 00 20     blr