block: Convert bdrv_refresh_total_sectors() to co_wrapper_mixed

BlockDriver->bdrv_getlength is categorized as IO callback, and it
currently doesn't run in a coroutine. We should let it take a graph
rdlock since the callback traverses the block nodes graph, which however
is only possible in a coroutine.

Therefore turn it into a co_wrapper to move the actual function into a
coroutine where the lock can be taken.

Because now this function creates a new coroutine and polls, we need to
take the AioContext lock where it is missing, for the only reason that
internally co_wrapper calls AIO_WAIT_WHILE and it expects to release the
AioContext lock.

This is especially messy when a co_wrapper creates a coroutine and polls
in bdrv_open_driver, because this function has so many callers in so
many context that it can easily lead to deadlocks. Therefore the new
rule for bdrv_open_driver is that the caller must always hold the
AioContext lock of the given bs (except if it is a coroutine), because
the function calls bdrv_refresh_total_sectors() which is now a
co_wrapper.

Once the rwlock is ultimated and placed in every place it needs to be,
we will poll using AIO_WAIT_WHILE_UNLOCKED and remove the AioContext
lock.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230113204212.359076-7-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index e493c28814..d4e360850f 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2332,10 +2332,15 @@ static void scsi_disk_reset(DeviceState *dev)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev.qdev, dev);
     uint64_t nb_sectors;
+    AioContext *ctx;
 
     scsi_device_purge_requests(&s->qdev, SENSE_CODE(RESET));
 
+    ctx = blk_get_aio_context(s->qdev.conf.blk);
+    aio_context_acquire(ctx);
     blk_get_geometry(s->qdev.conf.blk, &nb_sectors);
+    aio_context_release(ctx);
+
     nb_sectors /= s->qdev.blocksize / BDRV_SECTOR_SIZE;
     if (nb_sectors) {
         nb_sectors--;