Messages in this thread | | | Date | Mon, 31 Oct 2005 17:04:45 +0900 | From | Tejun Heo <> | Subject | Re: [PATCH][noop-iosched] don't reuse a freed request |
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Hi, guys.
Jens Axboe wrote: > 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. >
I'm currently debugging this. The problem is that we are using generic dispatch queue directly in the noop and merging is NOT allowed on dispatch queues but generic handling of last_merge tries to merge requests. I'm still trying to verify this, so I'll be back with results soon.
> >>--- 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. >
If the bug is where I think it is, I think the proper thing to do is to use separate list_head in noop instead of using generic dispatch queue directly thus making noop consistent with other ioscheds.
I'm more worried about oops w/ cfq Arnaldo reported in this thread. I'll track that down as soon as I'm done with this one.
Many bugs. Sorry. :-)
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