[Qemu-devel] [Bug 1708442] Re: Crash(assert) during reading image from http url through qemu-nbd

[Andrey Smetanin]

I've attached patch which resolves bug, but actually it's just
workaround and may be not unsafe, because it's just ignore assert.

** Patch added: "workaround patch"
   
https://bugs.launchpad.net/qemu/+bug/1708442/+attachment/4926546/+files/0001-util-async-ignore-self-co-enter-instead-of-assert.patch

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https://bugs.launchpad.net/bugs/1708442

Title:
  Crash(assert) during reading  image from http url through qemu-nbd

Status in QEMU:
  New

Bug description:
  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.

  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
  2) try read whole nbd device while error "blk_update_request: I/O error, dev 
nbd0, sector 42117" appears in dmesg

  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
  #16 0x000000000047730f in bdrv_driver_preadv (bs=0xf16820, offset=6556160, 
bytes=512, qiov=0x7f712d379b40, flags=0) at block/io.c:836
  #17 0x0000000000477c1f in bdrv_aligned_preadv (child=0xf1be20, 
req=0x7f712d379a60, offset=6556160, bytes=512, align=1,
      qiov=0x7f712d379b40, flags=0) at block/io.c:1086
  #18 0x0000000000478109 in bdrv_co_preadv (child=0xf1be20, offset=6556160, 
bytes=512, qiov=0x7f712d379b40, flags=0) at block/io.c:1180
  #19 0x0000000000437498 in qcow2_co_preadv (bs=0xf0fdc0, offset=21563904, 
bytes=512, qiov=0x7f712d379e80, flags=0)
      at block/qcow2.c:1812
  #20 0x000000000047730f in bdrv_driver_preadv (bs=0xf0fdc0, offset=21563904, 
bytes=512, qiov=0x7f712d379e80, flags=0)
      at block/io.c:836
  #21 0x0000000000477c1f in bdrv_aligned_preadv (child=0xf1c0d0, 
req=0x7f712d379d30, offset=21563904, bytes=512, align=1,
      qiov=0x7f712d379e80, flags=0) at block/io.c:1086
  #22 0x0000000000478109 in bdrv_co_preadv (child=0xf1c0d0, offset=21563904, 
bytes=512, qiov=0x7f712d379e80, flags=0)
      at block/io.c:1180
  #23 0x00000000004645ad in blk_co_preadv (blk=0xf1be90, offset=21563904, 
bytes=512, qiov=0x7f712d379e80, flags=0)
      at block/block-backend.c:991
  #24 0x00000000004646fa in blk_read_entry (opaque=0x7f712d379ea0) at 
block/block-backend.c:1038
  #25 0x000000000046481c in blk_prw (blk=0xf1be90, offset=21563904,
  ---Type <return> to continue, or q <return> to quit---
      buf=0xf7f000 
"2,NV\241t!\ti\312\vp\364\017Kl*\354\021\a\177\021\260\b\027\212\347\027\004\322\nG\340b\\\306pG\332\313\060\341;\002\360\063L\240\027T
 
\211\341\305\022АE\230\356DǮ}\211\bx\016\a\b\313\350\316\064.\017\372\032-R\376z\261\263\350|cQ<\016S_L\340A\221\366~L#\001+\271\204\065~\327\023\027I\211\343\361\276zT$4\336\273ˏ\353ʪ\234\016_Z|TMk\"\370\002\363~\334\332.\a\375\265mӌ{/%\304֎\374sF<E\371\031o&\202\217\226\276>I\356\302\375F\340\332\324\021\202\232>\026\261\233\303tv\023\304\006\243\037\062BϏ\b\324rs\360'"...,
 bytes=512, co_entry=0x4646aa <blk_read_entry>, flags=0) at 
block/block-backend.c:1074
  #26 0x0000000000464f81 in blk_pread (blk=0xf1be90, offset=21563904, 
buf=0xf7f000, count=512) at block/block-backend.c:1227
  #27 0x00000000004906cb in nbd_trip (opaque=0xf5a940) at nbd/server.c:1380
  #28 0x000000000051c0a5 in coroutine_trampoline (i0=15812176, i1=0) at 
util/coroutine-ucontext.c:79
  #29 0x00007f713143b5d0 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
  #30 0x00007f712d47a770 in ?? ()
  #31 0x0000000000000000 in ?? ()
  Backtrace stopped: Cannot access memory at address 0x7f712d37a000

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