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Re: [Qemu-devel] [Bug 1708442] [NEW] Crash(assert) during reading image
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [Bug 1708442] [NEW] Crash(assert) during reading image from http url through qemu-nbd |
Date: |
Thu, 3 Aug 2017 08:51:44 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 08/03/2017 07:12 AM, Andrey Smetanin wrote:
> Public bug reported:
>
> Description:
> During reading image from nbd device mounted by qemu-nbd server with url
> backend I/O error happens
> "blk_update_request: I/O error, dev nbd0, sector 42117" dmesg. After some
> investigation I found that qemu-nbd server aborts in aio_co_enter() assert in
> util/async.c:468.
>
Based on the backtrace, this looks to be a bug in the block/curl.c
driver, rather than the nbd/ or block/nbd.c code. If I'm right, it
should be possible to reproduce the crash using qemu-io directly on the
curl path, rather than adding the extra layer of an nbd client reading
through qemu-nbd (then again, having the qemu-nbd layer may be what is
allowing multiple parallel requests to hit the curl driver at once,
while qemu-io is not quite as easy to provoke into performing
complicated access patterns).
>
> Steps to reproduce:
>
> 1) sudo go run qemu-nbd-bug-report/qemu-nbd-bug.go (see qemu-nbd-bug-
> report.tar.gz)
>
> or try directly
>
> 1) qemu-nbd -c /dev/nbd0 -r -v --aio=native -f qcow2
> json:{"file.driver":"http","file.url":"http://localhost:9666/image","file.readahead":3276800
Presumably, you've got something serving the file at port 9666?
> 2) try read whole nbd device while error in dmesg appears x
>
> Versions:
>
> 1) qemu built from sources(/configure --target-list=x86_64-softmmu
> --disable-user --enable-curl --enable-linux-aio --enable-virtfs
> --enable-debug --disable-pie
> , top commit 5619c179057e24195ff19c8fe6d6a6cbcb16ed28):
>
> qemu-nbd -v
> qemu-nbd 2.9.90 (v2.10.0-rc0-67-g5619c17)
>
> 2) libcurl(built from sources, top commit
> 1767adf4399bb3be29121435e1bb1cc2bc05f7bf):
>
> curl -V
> curl 7.55.0-DEV (Linux) libcurl/7.55.0-DEV OpenSSL/1.0.2g zlib/1.2.8
>
>
> Backtrace:
> (gdb) bt
> #0 0x00007f7131426428 in __GI_raise (address@hidden) at
> ../sysdeps/unix/sysv/linux/raise.c:54
> #1 0x00007f713142802a in __GI_abort () at abort.c:89
> #2 0x00007f713141ebd7 in __assert_fail_base (fmt=<optimized out>,
> address@hidden "self != co",
> address@hidden "util/async.c", address@hidden,
> address@hidden <__PRETTY_FUNCTION__.24766> "aio_co_enter") at assert.c:92
> #3 0x00007f713141ec82 in __GI___assert_fail (assertion=0x54c924 "self !=
> co", file=0x54c871 "util/async.c", line=468,
> function=0x54c980 <__PRETTY_FUNCTION__.24766> "aio_co_enter") at
> assert.c:101
> #4 0x00000000004fe6a2 in aio_co_enter (ctx=0xf0ddb0, co=0xf14650) at
> util/async.c:468
> #5 0x00000000004fe637 in aio_co_wake (co=0xf14650) at util/async.c:456
> #6 0x0000000000495c8a in curl_read_cb (ptr=0xf566d9, size=1, nmemb=16135,
> opaque=0xf1cb90) at block/curl.c:275
> #7 0x00007f713242ac24 in Curl_client_chop_write () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #8 0x00007f713242ae03 in Curl_client_write () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #9 0x00007f713244e1cf in readwrite_data () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #10 0x00007f713244eb6f in Curl_readwrite () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #11 0x00007f713245c1bb in multi_runsingle () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #12 0x00007f713245d819 in multi_socket () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #13 0x00007f713245e067 in curl_multi_socket_action () from
> /usr/lib/x86_64-linux-gnu/libcurl.so
> #14 0x0000000000497555 in curl_setup_preadv (bs=0xf16820, acb=0x7f712d379860)
> at block/curl.c:918
> #15 0x00000000004975fb in curl_co_preadv (bs=0xf16820, offset=6556160,
> bytes=512, qiov=0x7f712d379b40, flags=0) at block/curl.c:935
The backtrace is definitely pointing at curl as being the problem.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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