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SubjectRe: Removing request from I/O scheduler queue
On Tue, Feb 27 2007, Swetha Krishnan wrote:
> I'm using linux 2.6.12 within user-mode linux. I need to remove a
> specific I/O request (that I have means to identify) from the I/O
> scheduler queues instead of moving it to the driver dispatch queue.
> To remove a request from the anticipatory scheduler's sort/fifo queues ,
> I'm making a call to as_remove_queued_request(), from within
> as_move_to_dispatch(). Before removing it, I invoke the
> as_find_next_arq() function so that the scheduler can pick the next
> request once this one is removed.
> Everything works fine as far as the remove is concerned, but after
> returning from the remove function and the end_io function that I call
> on the request's bio field(a dummy end_io), the scheduler fails to
> proceed with the next request chosen. I do check that if the next req
> chosen is NULL, I exit from the as_move_to_dispatch() function but even
> if I do this, the kernel panics after exiting from that function.
>
> The chief points of panic from the (larger) dump, seems to be
> a02277d0: [<a005eec3>] handle_IRQ_event+0x37/0x8c
> a0227800: [<a005efaf>] __do_IRQ+0x97/0xe0
> a0227820: [<a000defc>] do_IRQ+0x30/0x3c
>
> Could you give me any pointers as to why this is happening? Is there any
> additional cleanup that I need to do when I remove a request from the
> scheduler's queues that as_remove_queued_request() does not already do?
>
> I am rather new to linux I/O scheduling, so would be great if you could
> let me know if there something basic I'm missing here.

You need to show your code, nobody can help you with such a vague
description of what is going on. Either you are illegally removing a
request, or your removal code is buggy. That is about all that one can
conclude from the above.

--
Jens Axboe

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