[Bug 1916501] Re: qemu-img convert segfaults with specific URL

[Max Reitz]

I think I’ve come to kind of understood what might be wrong: qemu frees
CURLSocket objects when “their” transfer is done, but libcurl’s
documentation actually doesn’t note any long-lasting relationship
between a socket and some transfer (i.e., a CURL object), so we probably
shouldn’t free CURLSocket objects just because some transfer is done.
Instead, we should only do so once libcurl explicitly tells us to remove
the socket.

I’ve sent a two-patch series to that effect:
https://lists.nongnu.org/archive/html/qemu-block/2021-03/msg00515.html –
it seems to help.

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https://bugs.launchpad.net/bugs/1916501

Title:
  qemu-img convert segfaults with specific URL

Status in QEMU:
  New

Bug description:
  Using what is currently the latest git: (commit
  00d8ba9e0d62ea1c7459c25aeabf9c8bb7659462, Date:   Sun Feb 21 19:52:58
  2021 +0000)

  $ ./build/qemu-img convert -f qcow2 -O raw 
https://download.cirros-cloud.net/0.4.0/cirros-0.4.0-x86_64-disk.img out.img
  Segmentation fault (core dumped)

  
  Backtrace for convenience:
  qemu: qemu_mutex_lock_impl: Invalid argument

  Thread 1 "qemu-img" received signal SIGABRT, Aborted.
  0x00007ffff77c59d5 in raise () from /lib64/libc.so.6
  (gdb) bt
  #0  0x00007ffff77c59d5 in raise () from /lib64/libc.so.6
  #1  0x00007ffff77ae8a4 in abort () from /lib64/libc.so.6
  #2  0x00005555556705b2 in error_exit (err=<optimized out>, 
msg=msg@entry=0x5555556b69a0 <__func__.31> "qemu_mutex_lock_impl") at 
../util/qemu-thread-posix.c:37
  #3  0x0000555555670945 in qemu_mutex_lock_impl (mutex=0x555555ae3758, 
file=0x5555556827a2 "../block/curl.c", line=406) at 
../util/qemu-thread-posix.c:81
  #4  0x000055555559a05b in curl_multi_do (arg=0x555555aad2a0) at 
../block/curl.c:406
  #5  0x000055555566193a in aio_dispatch_handler (ctx=ctx@entry=0x555555737790, 
node=0x555555b14150) at ../util/aio-posix.c:329
  #6  0x0000555555662072 in aio_dispatch_handlers (ctx=0x555555737790) at 
../util/aio-posix.c:372
  #7  aio_dispatch (ctx=0x555555737790) at ../util/aio-posix.c:382
  #8  0x000055555564442e in aio_ctx_dispatch (source=<optimized out>, 
callback=<optimized out>, user_data=<optimized out>) at ../util/async.c:306
  #9  0x00007ffff7cfda9f in g_main_context_dispatch () from 
/lib64/libglib-2.0.so.0
  #10 0x000055555566f2c8 in glib_pollfds_poll () at ../util/main-loop.c:232
  #11 os_host_main_loop_wait (timeout=4397000000) at ../util/main-loop.c:255
  #12 main_loop_wait (nonblocking=nonblocking@entry=0) at 
../util/main-loop.c:531
  #13 0x0000555555581edd in convert_do_copy (s=0x7fffffffd3a0) at 
../qemu-img.c:2139
  #14 img_convert (argc=<optimized out>, argv=<optimized out>) at 
../qemu-img.c:2738
  #15 0x00005555555783b1 in main (argc=7, argv=<optimized out>) at 
../qemu-img.c:5536

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