Re: [Qemu-devel] [PATCH] Migration+TLS: Fix crash due to double cleanup

[Daniel P . Berrangé]

On Tue, May 01, 2018 at 11:00:35AM +0100, Daniel P. Berrangé wrote:
> On Mon, Apr 30, 2018 at 07:59:43PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > During a TLS connect we see:
> >   migration_channel_connect calls
> >   migration_tls_channel_connect
> >   (calls after TLS setup)
> >   migration_channel_connect
> > 
> > My previous error handling fix made migration_channel_connect
> > call migrate_fd_connect in all cases; unfortunately the above
> > means it gets called twice and crashes doing double cleanup.
> > 
> > Fixes: 688a3dcba98
> 
> This fixes the crash, but we're still seeing error messages duplicated
> 
> (qemu) migrate_set_parameter tls-creds tls0
> (qemu) migrate tcp:localhost:9000
> qemu-system-x86_64: Certificate does not match the hostname localhost
> qemu-system-x86_64: Certificate does not match the hostname localhost
> 
> git bisect points to 688a3dcba98 as the cause of these double
> errors still.

FYI the stack traces look like this..

The first error message is printed in this context:

#0  0x0000555555bb6c20 in error_report (fmt=0x555555d0d77e "%s") at 
util/qemu-error.c:273
#1  0x0000555555bb5fa5 in error_report_err (err=0x55555749cb00) at 
util/error.c:228
#2  0x0000555555a6d1f8 in migrate_fd_cleanup (address@hidden) at 
migration/migration.c:1106
#3  0x0000555555a6e2aa in migrate_fd_connect (address@hidden, 
error_in=0x55555768de80) at migration/migration.c:2387
#4  0x0000555555a6f8e7 in migration_channel_connect (address@hidden, 
address@hidden, address@hidden, error=<optimized out>) at migration/channel.c:83
#5  0x0000555555a6f2d6 in migration_tls_outgoing_handshake (task=<optimized 
out>, opaque=0x5555569925a0) at migration/tls.c:124
#6  0x0000555555b6d2b2 in qio_task_complete (address@hidden) at io/task.c:142
#7  0x0000555555b68c74 in qio_channel_tls_handshake_task (address@hidden, 
address@hidden) at io/channel-tls.c:171
#8  0x0000555555b6975a in qio_channel_tls_handshake (address@hidden, 
address@hidden <migration_tls_outgoing_handshake>, address@hidden, 
address@hidden) at io/channel-tls.c:215
#9  0x0000555555a6f6ac in migration_tls_channel_connect (address@hidden, 
address@hidden, address@hidden "localhost", address@hidden) at 
migration/tls.c:159
#10 0x0000555555a6f967 in migration_channel_connect (s=0x5555569925a0, 
address@hidden, hostname=0x555556bc0c30 "localhost", error=<optimized out>) at 
migration/channel.c:73
#11 0x0000555555a6e5f4 in socket_outgoing_migration (task=<optimized out>, 
opaque=0x555556cc7de0) at migration/socket.c:85
#12 0x0000555555b6d2b2 in qio_task_complete (address@hidden) at io/task.c:142
#13 0x0000555555b6d3a2 in gio_task_thread_result (opaque=0x5555578eff50) at 
io/task.c:88
#14 0x00007ffff5da1577 in g_idle_dispatch () at /lib64/libglib-2.0.so.0
#15 0x00007ffff5da4b77 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
#16 0x0000555555baf677 in glib_pollfds_poll () at util/main-loop.c:214
#17 0x0000555555baf677 in os_host_main_loop_wait (timeout=<optimized out>) at 
util/main-loop.c:261
#18 0x0000555555baf677 in main_loop_wait (nonblocking=<optimized out>) at 
util/main-loop.c:515
#19 0x00005555557b9157 in main_loop () at vl.c:1935
#20 0x00005555557b9157 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at vl.c:4767


The second error message is printed in this context:

#0  0x0000555555bb6c20 in error_report (address@hidden "%s") at 
util/qemu-error.c:273
#1  0x0000555555904035 in hmp_migrate_status_cb (opaque=0x555556bc0ba0) at 
hmp.c:1909
#2  0x0000555555baefac in timerlist_run_timers (timer_list=0x555556a0d760) at 
util/qemu-timer.c:536
#3  0x0000555555baf1b7 in qemu_clock_run_timers (type=QEMU_CLOCK_REALTIME) at 
util/qemu-timer.c:547
#4  0x0000555555baf1b7 in qemu_clock_run_all_timers () at util/qemu-timer.c:662
#5  0x0000555555baf69a in main_loop_wait (nonblocking=<optimized out>) at 
util/main-loop.c:521
#6  0x00005555557b9157 in main_loop () at vl.c:1935
#7  0x00005555557b9157 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at vl.c:4767


The second stack trace is the error reporting context that I added originally
in

  commit d59ce6f34434bf47a9b26138c908650bf9a24be1
  Author: Daniel P. Berrange <address@hidden>
  Date:   Wed Apr 27 11:05:00 2016 +0100

    migration: add reporting of errors for outgoing migration


So the first stack trace is the new duplicate.

Which error reporting context is "better" though, I don't know ?

My patch was based on the view that, although alot of code uses error_report,
long term all migration would eventually need to be able to filter an
'Error *errp' back up the stack, so that we can pass it back to QMP / HMP via
'info migrate' / query-migrate. So I decided to leave the error_report_err
call to the hmp.c code, as long term that's the only place that would need
to print to the console.


Regards,
Daniel
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