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SubjectRe: Elevator bug in concert with usb-storage


Fredrik Tolf wrote:

>Hello,
>
>I believe that there is a bug in the usb-storage code. I'm using
>2.6.0-test8-mm1, but I have experienced this in essentially all
>2.6.0-test* kernels. Mostly anytime when I remove a usb-storage device
>(especially before umounting it), I get a SEGV followed by general
>unstability in the SCSI subsys.
>
>After doing some research, I believe it is because the I/O scheduler
>is released before the SCSI subsys stops using it. Here is the SEGV
>report:
>
>Unable to handle kernel NULL pointer dereference at virtual address 00000001
> printing eip:
>00000001
>*pde = 00000000
>Oops: 0000 [#1]
>PREEMPT
>CPU: 0
>EIP: 0060:[<00000001>] Not tainted VLI
>EFLAGS: 00010202
>EIP is at 0x1
>eax: d8b83180 ebx: dafc4e00 ecx: 00000000 edx: dafc4e00
>esi: dafc4e10 edi: c03465e0 ebp: d990fe64 esp: d990fe58
>ds: 007b es: 007b ss: 0068
>Process umount (pid: 1744, threadinfo=d990e000 task=d8ba4080)
>Stack: c02173d7 dafc4e00 d8b83180 d990fe78 c0218f5d dafc4e00 df774800 c03465b0
> d990fe8c e0952fb5 dafc4e00 db8e3ca0 c03465b0 d990fe9c e0953f83 df774800
> 00000000 d990feac c021480a df774980 df7749a8 d990fec4 c01c26e3 df7749a8
>Call Trace:
> [<c02173d7>] elevator_exit+0x2d/0x3c
> [<c0218f5d>] blk_cleanup_queue+0x65/0x70
> [<e0952fb5>] scsi_free_sdev+0x11f/0x15a [scsi_mod]
> [<e0953f83>] scsi_device_dev_release+0x15/0x22 [scsi_mod]
> [<c021480a>] device_release+0x1a/0x60
> [<c01c26e3>] kobject_cleanup+0x63/0x70
> [<e094eb1c>] scsi_device_put+0x68/0xa6 [scsi_mod]
> [<e08a94cb>] sd_release+0x27/0x46 [sd_mod]
> [<c01569c5>] blkdev_put+0x1a7/0x1bc
> [<c015698f>] blkdev_put+0x171/0x1bc
> [<c015566b>] kill_block_super+0x25/0x2c
> [<c01548c7>] deactivate_super+0x67/0xae
> [<c01686c2>] sys_umount+0x36/0x84
> [<c014e9c5>] filp_close+0x43/0x66
> [<c016871d>] sys_oldumount+0xd/0x10
> [<c02bafeb>] syscall_call+0x7/0xb
>
>Code: Bad EIP value.
>
>It seems as if the elevator_exit_fn is set to 1, and there is a
>message logged just before the SEGV report spits out that an I/O
>scheduler is released, which makes me draw the conclusion that the
>kernel tries to free the I/O scheduler twice.
>
>My apologies for taking up your time if this is a known a fixed
>problem. However, if it is, can you point me to some information on
>how to remedy it?
>

James is having a look at refounting issues now. So it will be fixed.



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