Re: [Qemu-devel] [PATCH] m25p80: fix test on blk_pread() return value

[Eric Blake <eblake@redhat.com>]

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On 06/13/2016 11:43 AM, Cédric Le Goater wrote:
> On 06/13/2016 06:47 PM, Eric Blake wrote:
>> On 06/13/2016 10:25 AM, Cédric Le Goater wrote:
>>
>>>
>>> It seems that commit 243e6f69c129 ("m25p80: Switch to byte-based block access") 
>>> is bringing another issue :
>>>
>>> qemu-system-arm: /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1252: bdrv_aligned_pwritev: Assertion `!qiov || bytes == qiov->size' failed.
>>> Aborted (core dumped)
>>
>> Can you provide a more complete stack dump, 
> 
> yes, see below. 
> 
>> and/or a recipe on how to repeat the assertion?
> 
> That's more difficult right now. The patchset I am working on is not 
> mainline. It adds the SPI controller to the ast2400 soc and it uses 
> m25p80 flash modules with -mtdblock. 
> 
> I am trying to rebase on qemu's head to send it and I am hitting this 
> issue. So I need to find a simpler way to reproduce, with code only in
> mainline of course.
> 
> Until then, here is a gdb backtrace. Sorry about that.
> 

> #4  0x00007fa81c6694ac in bdrv_aligned_pwritev (bs=0x7fa81d4dd050, req=<optimized out>, offset=30878208, 
>     bytes=512, qiov=0x7fa7f47fee60, flags=0)
>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1243
> #5  0x00007fa81c669ecb in bdrv_co_pwritev (bs=0x7fa81d4dd050, offset=8, bytes=512, qiov=0x7fa80d5191c0, 
>     flags=(BDRV_REQ_COPY_ON_READ | BDRV_REQ_ZERO_WRITE | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_SERIALISING | BDRV_REQ_FUA | unknown: 4278124256), flags@entry=(unknown: 0))
>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1492

That 'flags' value looks bogus...

> #6  0x00007fa81c65e367 in blk_co_pwritev (blk=0x7fa81d4c5b60, offset=30878208, bytes=256, qiov=0x7fa80d5191c0, 
>     flags=(unknown: 0)) at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/block-backend.c:788
> #7  0x00007fa81c65e49b in blk_aio_write_entry (opaque=0x7fa7e849aca0)
>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/block-backend.c:977
> #8  0x00007fa81c6c823a in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>)
>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/util/coroutine-ucontext.c:78
> #9  0x00007fa818ea8f00 in ?? () from /lib/x86_64-linux-gnu/libc.so.6

and we don't get anything further in the backtrace beyond coroutines, to
see who's sending the bad parameters.  I recently debugged a bogus flags
in bdrv_aio_preadv, by hoisting an assert to occur before coroutines are
used in blk_aio_prwv():

https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg02948.html

I've just posted v2 of that patch (now a 2/2 series), but in v2 no
longer kept the assert at that point.  But maybe the correct fix, and/or
the hack for catching the bug prior to coroutines, will help you debug
where the bad arguments are coming from.


> #10 0x00007fa80d5189d0 in ?? ()
> #11 0x0000000000000000 in ?? ()
> (gdb) up 4
> #4  0x00007fa81c6694ac in bdrv_aligned_pwritev (bs=0x7fa81d4dd050, req=<optimized out>, offset=30878208, 
>     bytes=512, qiov=0x7fa7f47fee60, flags=0)
>     at /home/legoater/work/qemu/qemu-ast2400-mainline.git/block/io.c:1243
> 1243	    assert(!qiov || bytes == qiov->size);
> (gdb) p *qiov 
> $1 = {iov = 0x7fa81da671d0, niov = 1, nalloc = 1, size = 256}
> 
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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