[Qemu-devel] [Bug 1362635] Re: bdrv_read co-routine re-entered recursively

[senya]

the problem is taking place only when call bdrv_read frome separate
thread.

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https://bugs.launchpad.net/bugs/1362635

Title:
  bdrv_read co-routine re-entered recursively

Status in QEMU:
  New

Bug description:
  calling bdrv_read in a loop leads to the follwing situation:

  bs->drv->bdrv_aio_readv is called, and finally calls bdrv_co_io_em_complete 
in other thread context.
  there is a possibility of calling bdrv_co_io_em_complete before calling 
qemu_coroutine_yield in bdrv_co_io_em. And qemu fails with "co-routine 
re-entered recursively".

  static void bdrv_co_io_em_complete(void *opaque, int ret)
  {
      CoroutineIOCompletion *co = opaque;

      co->ret = ret;
      qemu_coroutine_enter(co->coroutine, NULL);
  }

  static int coroutine_fn bdrv_co_io_em(BlockDriverState *bs, int64_t 
sector_num,
                                        int nb_sectors, QEMUIOVector *iov,
                                        bool is_write)
  {
      CoroutineIOCompletion co = {
          .coroutine = qemu_coroutine_self(),
      };
      BlockDriverAIOCB *acb;

      if (is_write) {
          acb = bs->drv->bdrv_aio_writev(bs, sector_num, iov, nb_sectors,
                                         bdrv_co_io_em_complete, &co);
      } else {
          acb = bs->drv->bdrv_aio_readv(bs, sector_num, iov, nb_sectors,
                                        bdrv_co_io_em_complete, &co);
      }

      trace_bdrv_co_io_em(bs, sector_num, nb_sectors, is_write, acb);
      if (!acb) {
          return -EIO;
      }
      qemu_coroutine_yield();

      return co.ret;
  }

  is it a bug, or may be I don't understand something?

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