Re: [PATCH][noop-iosched] don't reuse a freed request
From: Tejun Heo
Date: Mon Oct 31 2005 - 03:05:05 EST
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. :-)
--
tejun
-
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