Re: [PATCH][noop-iosched] don't reuse a freed request

[Jens Axboe <axboe@suse.de>]

On Mon, Oct 31 2005, Arnaldo Carvalho de Melo wrote:
> Hi,
> 
> 	I'm getting the oops below when trying to use qemu with a kernel
> built with just the noop iosched, I'm never had looked at this code before,
> so I did a quick hack that seems enough for my case.
> 
> 	Ah, this is with a fairly recent git tree (today), haven't checked
> if it is present in 2.6.14.
> 
> Best Regards,
> 
> - Arnaldo
> 
> Unable to handle kernel paging request at virtual address c5f20f60
>  printing eip:
> c01b0ecd
> *pde = 00017067
> *pte = 05f20000
> Oops: 0000 [#1]
> DEBUG_PAGEALLOC
> Modules linked in:
> CPU:    0
> EIP:    0060:[<c01b0ecd>]    Not tainted VLI
> EFLAGS: 00000046   (2.6.14acme)
> EIP is at elv_rq_merge_ok+0x15/0x7b
> eax: 00000014   ebx: c5f20f58   ecx: 000003f8   edx: 00000046
> esi: c12a5a90   edi: c5f20f58   ebp: c11658d0   esp: c11658c4
> ds: 007b   es: 007b   ss: 0068
> Process swapper (pid: 1, threadinfo=c1165000 task=c1164af0)
> Stack: c0251883 c5ecfe4c c5d688c0 c1165904 c01b0f48 c5f20f58 c12a5a90 00000000
>        c5874000 c018c5e1 c5f15f24 0000002b 00000000 c5ecfe4c c5d688c0 c12a5a90
>        c1165920 c01b128d c5f20f58 c12a5a90 000a568a 00000000 00000002 c1165960
> Call Trace:
>  [<c0102a63>] show_stack+0x78/0x83
>  [<c0102b88>] show_registers+0x100/0x167
>  [<c0102d35>] die+0xcb/0x140
>  [<c0234308>] do_page_fault+0x393/0x53a
>  [<c0102777>] error_code+0x4f/0x54
>  [<c01b0f48>] elv_try_merge+0x15/0x84
>  [<c01b128d>] elv_merge+0x1d/0x4f
>  [<c01b41d9>] __make_request+0xb2/0x425
>  [<c01b46f9>] generic_make_request+0x125/0x137

Hrmpf, this looks really bad. Tejun, clearly there are still paths where
->last_rq isn't being cleared.

> --- a/drivers/block/ll_rw_blk.c
> +++ b/drivers/block/ll_rw_blk.c
> @@ -1787,6 +1787,9 @@ static inline void blk_free_request(requ
>  	if (rq->flags & REQ_ELVPRIV)
>  		elv_put_request(q, rq);
>  	mempool_free(rq, q->rq.rq_pool);
> +
> +	if (rq == q->last_merge)
> +		q->last_merge = NULL;
>  }
>  
>  static inline struct request *

It's most likely a bug getting this far in the first place, but does it
fix things for you? I'll get on this asap.

-- 
Jens Axboe

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