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qemu crashes with trap when negative number used for maxcpus #16

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nasastry opened this issue Oct 10, 2017 · 5 comments
Closed

qemu crashes with trap when negative number used for maxcpus #16

nasastry opened this issue Oct 10, 2017 · 5 comments

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@nasastry
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nasastry commented Oct 10, 2017 •
edited by cdeadmin
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cde:info Mirrored with LTC bug https://bugzilla.linux.ibm.com/show_bug.cgi?id=159921 </cde:info>

Run qemu with maxcpus with negative number.

# /usr/bin/qemu-system-ppc64 --nographic -vga none -machine pseries,accel=kvm,kvm-type=HV -m 2G,slots=32,maxmem=16G -device virtio-blk-pci,drive=rootdisk -drive file=/home/nasastry/hostos-3.0-ppc64le.qcow2,if=none,cache=none,id=rootdisk,format=qcow2 -net nic,model=virtio -smp 8,cores=1,threads=1,maxcpus=-12

(process:26151): GLib-ERROR **: gmem.c:130: failed to allocate 18446744073709550568 bytes
Trace/breakpoint trap

Though issue #15 and this looks similar by error message. Code changes needed in different places.
@nasastry nasastry changed the title qemu crashes with trap negative number used for maxcpus qemu crashes with trap when negative number used for maxcpus Oct 10, 2017
@sathnaga
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sathnaga commented Oct 10, 2017 •
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This hits in upstream qemu aswell, qemu@530049b

 ./ppc64-softmmu/qemu-system-ppc64 -M pseries,max-cpu-compat=power9  -smp 8,threads=1,cores=1,maxcpus=-1 -m 8192 -nographic -enable-kvm /home/sath/hostos-3.0-ppc64le.qcow2 -monitor stdio -serial /dev/pts/3
QEMU 2.10.50 monitor - type 'help' for more information
(qemu) 
(process:38588): GLib-ERROR **: gmem.c:130: failed to allocate 18446744073709551536 bytes
Trace/breakpoint trap

@sathnaga
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sathnaga commented Oct 10, 2017 •
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0001-Fixup-Add-check-for-negative-vcpu-values.txt

Tried fixing it , let me know if approach is fine, will send it upstream, Thanks in advance

@cdeadmin
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Tried fixing it in qemu, let me know if approach is fine, will send it upstream, Thanks in advance

@nasastry nasastry mentioned this issue Oct 12, 2017
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@nasastry nasastry mentioned this issue Oct 30, 2017
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aik pushed a commit that referenced this issue Jan 31, 2018
@cheney-lin @bonzini
qemu-thread: fix races on threads that exit very quickly
68a9398 
If we create a thread with QEMU_THREAD_DETACHED mode, QEMU may get a segfault with low probability.

The backtrace is:
   #0  0x00007f46c60291d7 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56
   #1  0x00007f46c602a8c8 in __GI_abort () at abort.c:90
   #2  0x00000000008543c9 in PAT_abort ()
   #3  0x000000000085140d in patchIllInsHandler ()
   #4  <signal handler called>
   #5  pthread_detach (th=139933037614848) at pthread_detach.c:50
   #6  0x0000000000829759 in qemu_thread_create (thread=thread@entry=0x7ffdaa8205e0, name=name@entry=0x94d94a "io-task-worker", start_routine=start_routine@entry=0x7eb9a0 <qio_task_thread_worker>,
       arg=arg@entry=0x3f5cf70, mode=mode@entry=1) at util/qemu_thread_posix.c:512
   #7  0x00000000007ebc96 in qio_task_run_in_thread (task=0x31db2c0, worker=worker@entry=0x7e7e40 <qio_channel_socket_connect_worker>, opaque=0xcd23380, destroy=0x7f1180 <qapi_free_SocketAddress>)
       at io/task.c:141
   #8  0x00000000007e7f33 in qio_channel_socket_connect_async (ioc=ioc@entry=0x626c0b0, addr=<optimized out>, callback=callback@entry=0x55e080 <qemu_chr_socket_connected>, opaque=opaque@entry=0x42862c0,
       destroy=destroy@entry=0x0) at io/channel_socket.c:194
   #9  0x000000000055bdd1 in socket_reconnect_timeout (opaque=0x42862c0) at qemu_char.c:4744
   #10 0x00007f46c72483b3 in g_timeout_dispatch () from /usr/lib64/libglib-2.0.so.0
   #11 0x00007f46c724799a in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
   #12 0x000000000076c646 in glib_pollfds_poll () at main_loop.c:228
   #13 0x000000000076c6eb in os_host_main_loop_wait (timeout=348000000) at main_loop.c:273
   #14 0x000000000076c815 in main_loop_wait (nonblocking=nonblocking@entry=0) at main_loop.c:521
   #15 0x000000000056a511 in main_loop () at vl.c:2076
   #16 0x0000000000420705 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4940

The cause of this problem is a glibc bug; for more information, see
https://sourceware.org/bugzilla/show_bug.cgi?id=19951.
The solution for this bug is to use pthread_attr_setdetachstate.

There is a similar issue with pthread_setname_np, which is moved
from creating thread to created thread.

Signed-off-by: linzhecheng <linzhecheng@huawei.com>
Message-Id: <20171128044656.10592-1-linzhecheng@huawei.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
[Simplify the code by removing qemu_thread_set_name, and free the arguments
 before invoking the start routine. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aik pushed a commit that referenced this issue Jan 31, 2018
@elmarco @bonzini
readline: add a free function
e5dc1a6 
Fixes leaks such as:

Direct leak of 2 byte(s) in 1 object(s) allocated from:
    #0 0x7eff58beb850 in malloc (/lib64/libasan.so.4+0xde850)
    #1 0x7eff57942f0c in g_malloc ../glib/gmem.c:94
    #2 0x7eff579431cf in g_malloc_n ../glib/gmem.c:331
    #3 0x7eff5795f6eb in g_strdup ../glib/gstrfuncs.c:363
    #4 0x55db720f1d46 in readline_hist_add /home/elmarco/src/qq/util/readline.c:258
    #5 0x55db720f2d34 in readline_handle_byte /home/elmarco/src/qq/util/readline.c:387
    #6 0x55db71539d00 in monitor_read /home/elmarco/src/qq/monitor.c:3896
    #7 0x55db71f9be35 in qemu_chr_be_write_impl /home/elmarco/src/qq/chardev/char.c:167
    #8 0x55db71f9bed3 in qemu_chr_be_write /home/elmarco/src/qq/chardev/char.c:179
    #9 0x55db71fa013c in fd_chr_read /home/elmarco/src/qq/chardev/char-fd.c:66
    #10 0x55db71fe18a8 in qio_channel_fd_source_dispatch /home/elmarco/src/qq/io/channel-watch.c:84
    #11 0x7eff5793a90b in g_main_dispatch ../glib/gmain.c:3182
    #12 0x7eff5793b7ac in g_main_context_dispatch ../glib/gmain.c:3847
    #13 0x55db720af3bd in glib_pollfds_poll /home/elmarco/src/qq/util/main-loop.c:214
    #14 0x55db720af505 in os_host_main_loop_wait /home/elmarco/src/qq/util/main-loop.c:261
    #15 0x55db720af6d6 in main_loop_wait /home/elmarco/src/qq/util/main-loop.c:515
    #16 0x55db7184e0de in main_loop /home/elmarco/src/qq/vl.c:1995
    #17 0x55db7185e956 in main /home/elmarco/src/qq/vl.c:4914
    #18 0x7eff4ea17039 in __libc_start_main (/lib64/libc.so.6+0x21039)

(while at it, use g_new0(ReadLineState), it's a bit easier to read)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180104160523.22995-11-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aik pushed a commit that referenced this issue Jan 31, 2018
@elmarco @bonzini
qemu-config: fix leak in query-command-line-options
b11e20f 
Direct leak of 160 byte(s) in 4 object(s) allocated from:
    #0 0x55ed7678cda8 in calloc (/home/elmarco/src/qq/build/x86_64-softmmu/qemu-system-x86_64+0x797da8)
    #1 0x7f3f5e725f75 in g_malloc0 /home/elmarco/src/gnome/glib/builddir/../glib/gmem.c:124
    #2 0x55ed778aa3a7 in query_option_descs /home/elmarco/src/qq/util/qemu-config.c:60:16
    #3 0x55ed778aa307 in get_drive_infolist /home/elmarco/src/qq/util/qemu-config.c:140:19
    #4 0x55ed778a9f40 in qmp_query_command_line_options /home/elmarco/src/qq/util/qemu-config.c:254:36
    #5 0x55ed76d4868c in qmp_marshal_query_command_line_options /home/elmarco/src/qq/build/qmp-marshal.c:3078:14
    #6 0x55ed77855dd5 in do_qmp_dispatch /home/elmarco/src/qq/qapi/qmp-dispatch.c:104:5
    #7 0x55ed778558cc in qmp_dispatch /home/elmarco/src/qq/qapi/qmp-dispatch.c:131:11
    #8 0x55ed768b592f in handle_qmp_command /home/elmarco/src/qq/monitor.c:3840:11
    #9 0x55ed7786ccfe in json_message_process_token /home/elmarco/src/qq/qobject/json-streamer.c:105:5
    #10 0x55ed778fe37c in json_lexer_feed_char /home/elmarco/src/qq/qobject/json-lexer.c:323:13
    #11 0x55ed778fdde6 in json_lexer_feed /home/elmarco/src/qq/qobject/json-lexer.c:373:15
    #12 0x55ed7786cd83 in json_message_parser_feed /home/elmarco/src/qq/qobject/json-streamer.c:124:12
    #13 0x55ed768b559e in monitor_qmp_read /home/elmarco/src/qq/monitor.c:3882:5
    #14 0x55ed77714f29 in qemu_chr_be_write_impl /home/elmarco/src/qq/chardev/char.c:167:9
    #15 0x55ed77714fde in qemu_chr_be_write /home/elmarco/src/qq/chardev/char.c:179:9
    #16 0x55ed7772ffad in tcp_chr_read /home/elmarco/src/qq/chardev/char-socket.c:440:13
    #17 0x55ed7777113b in qio_channel_fd_source_dispatch /home/elmarco/src/qq/io/channel-watch.c:84:12
    #18 0x7f3f5e71d90b in g_main_dispatch /home/elmarco/src/gnome/glib/builddir/../glib/gmain.c:3182
    #19 0x7f3f5e71e7ac in g_main_context_dispatch /home/elmarco/src/gnome/glib/builddir/../glib/gmain.c:3847
    #20 0x55ed77886ffc in glib_pollfds_poll /home/elmarco/src/qq/util/main-loop.c:214:9
    #21 0x55ed778865fd in os_host_main_loop_wait /home/elmarco/src/qq/util/main-loop.c:261:5
    #22 0x55ed77886222 in main_loop_wait /home/elmarco/src/qq/util/main-loop.c:515:11
    #23 0x55ed76d2a4df in main_loop /home/elmarco/src/qq/vl.c:1995:9
    #24 0x55ed76d1cb4a in main /home/elmarco/src/qq/vl.c:4914:5
    #25 0x7f3f555f6039 in __libc_start_main (/lib64/libc.so.6+0x21039)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180104160523.22995-14-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
aik pushed a commit that referenced this issue Jan 31, 2018
@elmarco @bonzini
disas/s390: fix global-buffer-overflow
02a2ad2 
Spotted thanks to ASAN:

==25226==ERROR: AddressSanitizer: global-buffer-overflow on address 0x556715a1f120 at pc 0x556714b6f6b1 bp 0x7ffcdfac1360 sp 0x7ffcdfac1350
READ of size 1 at 0x556715a1f120 thread T0
    #0 0x556714b6f6b0 in init_disasm /home/elmarco/src/qemu/disas/s390.c:219
    #1 0x556714b6fa6a in print_insn_s390 /home/elmarco/src/qemu/disas/s390.c:294
    #2 0x55671484d031 in monitor_disas /home/elmarco/src/qemu/disas.c:635
    #3 0x556714862ec0 in memory_dump /home/elmarco/src/qemu/monitor.c:1324
    #4 0x55671486342a in hmp_memory_dump /home/elmarco/src/qemu/monitor.c:1418
    #5 0x5567148670be in handle_hmp_command /home/elmarco/src/qemu/monitor.c:3109
    #6 0x5567148674ed in qmp_human_monitor_command /home/elmarco/src/qemu/monitor.c:613
    #7 0x556714b00918 in qmp_marshal_human_monitor_command /home/elmarco/src/qemu/build/qmp-marshal.c:1704
    #8 0x556715138a3e in do_qmp_dispatch /home/elmarco/src/qemu/qapi/qmp-dispatch.c:104
    #9 0x556715138f83 in qmp_dispatch /home/elmarco/src/qemu/qapi/qmp-dispatch.c:131
    #10 0x55671485cf88 in handle_qmp_command /home/elmarco/src/qemu/monitor.c:3839
    #11 0x55671514e80b in json_message_process_token /home/elmarco/src/qemu/qobject/json-streamer.c:105
    #12 0x5567151bf2dc in json_lexer_feed_char /home/elmarco/src/qemu/qobject/json-lexer.c:323
    #13 0x5567151bf827 in json_lexer_feed /home/elmarco/src/qemu/qobject/json-lexer.c:373
    #14 0x55671514ee62 in json_message_parser_feed /home/elmarco/src/qemu/qobject/json-streamer.c:124
    #15 0x556714854b1f in monitor_qmp_read /home/elmarco/src/qemu/monitor.c:3881
    #16 0x556715045440 in qemu_chr_be_write_impl /home/elmarco/src/qemu/chardev/char.c:172
    #17 0x556715047184 in qemu_chr_be_write /home/elmarco/src/qemu/chardev/char.c:184
    #18 0x55671505a8e6 in tcp_chr_read /home/elmarco/src/qemu/chardev/char-socket.c:440
    #19 0x5567150943c3 in qio_channel_fd_source_dispatch /home/elmarco/src/qemu/io/channel-watch.c:84
    #20 0x7fb90292b90b in g_main_dispatch ../glib/gmain.c:3182
    #21 0x7fb90292c7ac in g_main_context_dispatch ../glib/gmain.c:3847
    #22 0x556715162eca in glib_pollfds_poll /home/elmarco/src/qemu/util/main-loop.c:214
    #23 0x556715163001 in os_host_main_loop_wait /home/elmarco/src/qemu/util/main-loop.c:261
    #24 0x5567151631fa in main_loop_wait /home/elmarco/src/qemu/util/main-loop.c:515
    #25 0x556714ad6d3b in main_loop /home/elmarco/src/qemu/vl.c:1950
    #26 0x556714ade329 in main /home/elmarco/src/qemu/vl.c:4865
    #27 0x7fb8fe5c9009 in __libc_start_main (/lib64/libc.so.6+0x21009)
    #28 0x5567147af4d9 in _start (/home/elmarco/src/qemu/build/s390x-softmmu/qemu-system-s390x+0xf674d9)

0x556715a1f120 is located 32 bytes to the left of global variable 'char_hci_type_info' defined in '/home/elmarco/src/qemu/hw/bt/hci-csr.c:493:23' (0x556715a1f140) of size 104
0x556715a1f120 is located 8 bytes to the right of global variable 's390_opcodes' defined in '/home/elmarco/src/qemu/disas/s390.c:860:33' (0x556715a15280) of size 40600

This fix is based on Andreas Arnez <arnez@linux.vnet.ibm.com> upstream
commit:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=9ace48f3d7d80ce09c5df60cccb433470410b11b

2014-08-19  Andreas Arnez  <arnez@linux.vnet.ibm.com>

       * s390-dis.c (init_disasm): Simplify initialization of
       opc_index[].  This also fixes an access after the last element
       of s390_opcodes[].

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180104160523.22995-19-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
@cdeadmin
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cdeadmin commented Feb 2, 2018

------- Comment From alexey@au1.ibm.com 2018-02-01 22:34:15 EDT-------
Fixed by upstream,
"-smp 8,cores=1,threads=1,maxcpus=-12 " produces
qemu-system-ppc64: Invalid SMP CPUs -12. The max CPUs supported by machine 'pseries-2.12' is 1024

and does not crash any more.

@cdeadmin
Copy link

------- Comment From nasastry@in.ibm.com 2018-02-15 04:00:52 EDT-------
With qemu-system-ppc-2.11.0-1.rel.gite7153e0.el7.centos.ppc64le

qemu process quits with a proper error. This bugzilla can be closed.

/usr/bin/qemu-system-ppc64 --nographic -vga none -machine pseries,accel=kvm,kvm-type=HV -m 2G,slots=32,maxmem=16G -device virtio-blk-pci,drive=rootdisk -drive file=/home/nasastry/hostos-3.0-ppc64le.qcow2,if=none,cache=none,id=rootdisk,format=qcow2 -net nic,model=virtio -smp 8,cores=1,threads=1,maxcpus=-12

qemu-system-ppc64: Invalid SMP CPUs -12. The max CPUs supported by machine 'pseries-2.11' is 1024

aik pushed a commit that referenced this issue Mar 29, 2018
@elmarco @dagrh
migration: fix minor finalize leak
ab105cc 
Spotted thanks to ASAN:
QTEST_QEMU_BINARY=x86_64-softmmu/qemu-system-x86_64 tests/migration-test -p /x86_64/migration/bad_dest

==30302==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 48 byte(s) in 1 object(s) allocated from:
    #0 0x7f60efba1a38 in __interceptor_calloc (/lib64/libasan.so.4+0xdea38)
    #1 0x7f60eef3cf75 in g_malloc0 ../glib/gmem.c:124
    #2 0x55ca9094702c in error_copy /home/elmarco/src/qemu/util/error.c:203
    #3 0x55ca9037a30f in migrate_set_error /home/elmarco/src/qemu/migration/migration.c:1139
    #4 0x55ca9037a462 in migrate_fd_error /home/elmarco/src/qemu/migration/migration.c:1150
    #5 0x55ca9038162b in migrate_fd_connect /home/elmarco/src/qemu/migration/migration.c:2411
    #6 0x55ca90386e41 in migration_channel_connect /home/elmarco/src/qemu/migration/channel.c:81
    #7 0x55ca9038335e in socket_outgoing_migration /home/elmarco/src/qemu/migration/socket.c:85
    #8 0x55ca9083dd3a in qio_task_complete /home/elmarco/src/qemu/io/task.c:142
    #9 0x55ca9083d6cc in gio_task_thread_result /home/elmarco/src/qemu/io/task.c:88
    #10 0x7f60eef37317 in g_idle_dispatch ../glib/gmain.c:5552
    #11 0x7f60eef3490b in g_main_dispatch ../glib/gmain.c:3182
    #12 0x7f60eef357ac in g_main_context_dispatch ../glib/gmain.c:3847
    #13 0x55ca90927231 in glib_pollfds_poll /home/elmarco/src/qemu/util/main-loop.c:214
    #14 0x55ca90927420 in os_host_main_loop_wait /home/elmarco/src/qemu/util/main-loop.c:261
    #15 0x55ca909275fa in main_loop_wait /home/elmarco/src/qemu/util/main-loop.c:515
    #16 0x55ca8fc1c2a4 in main_loop /home/elmarco/src/qemu/vl.c:1942
    #17 0x55ca8fc2eb3a in main /home/elmarco/src/qemu/vl.c:4724
    #18 0x7f60e4082009 in __libc_start_main (/lib64/libc.so.6+0x21009)

Indirect leak of 45 byte(s) in 1 object(s) allocated from:
    #0 0x7f60efba1850 in malloc (/lib64/libasan.so.4+0xde850)
    #1 0x7f60eef3cf0c in g_malloc ../glib/gmem.c:94
    #2 0x7f60eef3d1cf in g_malloc_n ../glib/gmem.c:331
    #3 0x7f60eef596eb in g_strdup ../glib/gstrfuncs.c:363
    #4 0x55ca90947085 in error_copy /home/elmarco/src/qemu/util/error.c:204
    #5 0x55ca9037a30f in migrate_set_error /home/elmarco/src/qemu/migration/migration.c:1139
    #6 0x55ca9037a462 in migrate_fd_error /home/elmarco/src/qemu/migration/migration.c:1150
    #7 0x55ca9038162b in migrate_fd_connect /home/elmarco/src/qemu/migration/migration.c:2411
    #8 0x55ca90386e41 in migration_channel_connect /home/elmarco/src/qemu/migration/channel.c:81
    #9 0x55ca9038335e in socket_outgoing_migration /home/elmarco/src/qemu/migration/socket.c:85
    #10 0x55ca9083dd3a in qio_task_complete /home/elmarco/src/qemu/io/task.c:142
    #11 0x55ca9083d6cc in gio_task_thread_result /home/elmarco/src/qemu/io/task.c:88
    #12 0x7f60eef37317 in g_idle_dispatch ../glib/gmain.c:5552
    #13 0x7f60eef3490b in g_main_dispatch ../glib/gmain.c:3182
    #14 0x7f60eef357ac in g_main_context_dispatch ../glib/gmain.c:3847
    #15 0x55ca90927231 in glib_pollfds_poll /home/elmarco/src/qemu/util/main-loop.c:214
    #16 0x55ca90927420 in os_host_main_loop_wait /home/elmarco/src/qemu/util/main-loop.c:261
    #17 0x55ca909275fa in main_loop_wait /home/elmarco/src/qemu/util/main-loop.c:515
    #18 0x55ca8fc1c2a4 in main_loop /home/elmarco/src/qemu/vl.c:1942
    #19 0x55ca8fc2eb3a in main /home/elmarco/src/qemu/vl.c:4724
    #20 0x7f60e4082009 in __libc_start_main (/lib64/libc.so.6+0x21009)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180306170959.3921-1-marcandre.lureau@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
aik pushed a commit that referenced this issue May 15, 2018
@xzpeter @ebblake
monitor: bind dispatch bh to iohandler context
951702f 
Eric Auger reported the problem days ago that OOB broke ARM when running
with libvirt:

http://lists.gnu.org/archive/html/qemu-devel/2018-03/msg06231.html

The problem was that the monitor dispatcher bottom half was bound to
qemu_aio_context now, which could be polled unexpectedly in block code.
We should keep the dispatchers run in iohandler_ctx just like what we
did before the Out-Of-Band series (chardev uses qio, and qio binds
everything with iohandler_ctx).

If without this change, QMP dispatcher might be run even before reaching
main loop in block IO path, for example, in a stack like (the ARM case,
"cont" command handler run even during machine init phase):

        #0  qmp_cont ()
        #1  0x00000000006bd210 in qmp_marshal_cont ()
        #2  0x0000000000ac05c4 in do_qmp_dispatch ()
        #3  0x0000000000ac07a0 in qmp_dispatch ()
        #4  0x0000000000472d60 in monitor_qmp_dispatch_one ()
        #5  0x000000000047302c in monitor_qmp_bh_dispatcher ()
        #6  0x0000000000acf374 in aio_bh_call ()
        #7  0x0000000000acf428 in aio_bh_poll ()
        #8  0x0000000000ad5110 in aio_poll ()
        #9  0x0000000000a08ab8 in blk_prw ()
        #10 0x0000000000a091c4 in blk_pread ()
        #11 0x0000000000734f94 in pflash_cfi01_realize ()
        #12 0x000000000075a3a4 in device_set_realized ()
        #13 0x00000000009a26cc in property_set_bool ()
        #14 0x00000000009a0a40 in object_property_set ()
        #15 0x00000000009a3a08 in object_property_set_qobject ()
        #16 0x00000000009a0c8c in object_property_set_bool ()
        #17 0x0000000000758f94 in qdev_init_nofail ()
        #18 0x000000000058e190 in create_one_flash ()
        #19 0x000000000058e2f4 in create_flash ()
        #20 0x00000000005902f0 in machvirt_init ()
        #21 0x00000000007635cc in machine_run_board_init ()
        #22 0x00000000006b135c in main ()

Actually the problem is more severe than that.  After we switched to the
qemu AIO handler it means the monitor dispatcher code can even be called
with nested aio_poll(), then it can be an explicit aio_poll() inside
another main loop aio_poll() which could be racy too; breaking code
like TPM and 9p that use nested event loops.

Switch to use the iohandler_ctx for monitor dispatchers.

My sincere thanks to Eric Auger who offered great help during both
debugging and verifying the problem.  The ARM test was carried out by
applying this patch upon QEMU 2.12.0-rc0 and problem is gone after the
patch.

A quick test of mine shows that after this patch applied we can pass all
raw iotests even with OOB on by default.

CC: Eric Blake <eblake@redhat.com>
CC: Markus Armbruster <armbru@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Fam Zheng <famz@redhat.com>
Reported-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20180410044942.17059-1-peterx@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
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