qemu/nbd
Sergio Lopez f148ae7d36 nbd/server: Quiesce coroutines on context switch
When switching between AIO contexts we need to me make sure that both
recv_coroutine and send_coroutine are not scheduled to run. Otherwise,
QEMU may crash while attaching the new context with an error like
this one:

aio_co_schedule: Co-routine was already scheduled in 'aio_co_schedule'

To achieve this we need a local implementation of
'qio_channel_readv_all_eof' named 'nbd_read_eof' (a trick already done
by 'nbd/client.c') that allows us to interrupt the operation and to
know when recv_coroutine is yielding.

With this in place, we delegate detaching the AIO context to the
owning context with a BH ('nbd_aio_detach_bh') scheduled using
'aio_wait_bh_oneshot'. This BH signals that we need to quiesce the
channel by setting 'client->quiescing' to 'true', and either waits for
the coroutine to finish using AIO_WAIT_WHILE or, if it's yielding in
'nbd_read_eof', actively enters the coroutine to interrupt it.

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1900326
Signed-off-by: Sergio Lopez <slp@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201214170519.223781-4-slp@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
2021-01-20 14:48:54 -06:00
..
client.c nbd: Use ERRP_GUARD() 2020-07-10 15:18:09 +02:00
common.c nbd: Prepare for NBD_CMD_FLAG_FAST_ZERO 2019-09-05 16:03:13 -05:00
meson.build block: move block exports to libblockdev 2020-10-23 13:42:16 +01:00
nbd-internal.h configure: Add a proper check for sys/ioccom.h and use it in tpm_ioctl.h 2020-11-17 09:45:24 +01:00
server.c nbd/server: Quiesce coroutines on context switch 2021-01-20 14:48:54 -06:00
trace-events trace: Remove trailing newline in events 2019-09-18 10:19:47 +01:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00