virtio: Drop out of coroutine context in virtio_load()

virtio: Drop out of coroutine context in virtio_load()

virtio_load() as a whole should run in coroutine context because it
reads from the migration stream and we don't want this to block.

However, it calls virtio_set_features_nocheck() and devices don't
expect their .set_features callback to run in a coroutine and therefore
call functions that may not be called in coroutine context. To fix this,
drop out of coroutine context for calling virtio_set_features_nocheck().

Without this fix, the following crash was reported:

  #0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
  #1  0x00007efc738c05d3 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
  #2  0x00007efc73873d26 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
  #3  0x00007efc738477f3 in __GI_abort () at abort.c:79
  #4  0x00007efc7384771b in __assert_fail_base (fmt=0x7efc739dbcb8 "", assertion=assertion@entry=0x560aebfbf5cf "!qemu_in_coroutine()",
     file=file@entry=0x560aebfcd2d4 "../block/graph-lock.c", line=line@entry=275, function=function@entry=0x560aebfcd34d "void bdrv_graph_rdlock_main_loop(void)") at assert.c:92
  #5  0x00007efc7386ccc6 in __assert_fail (assertion=0x560aebfbf5cf "!qemu_in_coroutine()", file=0x560aebfcd2d4 "../block/graph-lock.c", line=275,
     function=0x560aebfcd34d "void bdrv_graph_rdlock_main_loop(void)") at assert.c:101
  #6  0x0000560aebcd8dd6 in bdrv_register_buf ()
  #7  0x0000560aeb97ed97 in ram_block_added.llvm ()
  #8  0x0000560aebb8303f in ram_block_add.llvm ()
  #9  0x0000560aebb834fa in qemu_ram_alloc_internal.llvm ()
  #10 0x0000560aebb2ac98 in vfio_region_mmap ()
  #11 0x0000560aebb3ea0f in vfio_bars_register ()
  #12 0x0000560aebb3c628 in vfio_realize ()
  #13 0x0000560aeb90f0c2 in pci_qdev_realize ()
  #14 0x0000560aebc40305 in device_set_realized ()
  #15 0x0000560aebc48e07 in property_set_bool.llvm ()
  #16 0x0000560aebc46582 in object_property_set ()
  #17 0x0000560aebc4cd58 in object_property_set_qobject ()
  #18 0x0000560aebc46ba7 in object_property_set_bool ()
  #19 0x0000560aeb98b3ca in qdev_device_add_from_qdict ()
  #20 0x0000560aebb1fbaf in virtio_net_set_features ()
  #21 0x0000560aebb46b51 in virtio_set_features_nocheck ()
  #22 0x0000560aebb47107 in virtio_load ()
  #23 0x0000560aeb9ae7ce in vmstate_load_state ()
  #24 0x0000560aeb9d2ee9 in qemu_loadvm_state_main ()
  #25 0x0000560aeb9d45e1 in qemu_loadvm_state ()
  #26 0x0000560aeb9bc32c in process_incoming_migration_co.llvm ()
  #27 0x0000560aebeace56 in coroutine_trampoline.llvm ()

Cc: qemu-stable@nongnu.org
Buglink: https://issues.redhat.com/browse/RHEL-832
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230905145002.46391-3-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 92e2e6a867334a990f8d29f07ca34e3162fdd6ec)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: remove coroutine_mixed_fn markings introduced in v7.2.0-909-g0f3de970fe)