Re: [PATCH] linux-aio: add IO_CMD_FDSYNC command support

[Prasad Pandit]

Hello Kevin,

On Fri, 8 Mar 2024 at 17:38, Prasad Pandit <ppandit@redhat.com> wrote:
> I'm trying to test it against the Fedora-26 kernel, which was < 4.13.0, and 
> did not support the AIO_FDSYNC call.

[PATCH v2] -> 
https://lists.nongnu.org/archive/html/qemu-devel/2024-03/msg02495.html

* I've sent v2 of this patch which checks the return value from
'laio_co_submit' function and returns if it is >= zero(0).

* I tested this and previous version of this patch on host kernels
which support IO_CMD_FDSYNC and which don't.
    1) When kernel supports IO_CMD_FDSYNC, everything works well. No issues.

   2) When kernel does _not_ support IO_CMD_FDSYNC
        - With [PATCH v1], guest does not boot, instead it opens a rescue shell
        - With [PATCH v2], guest boots and seems to work fine. But
after some time guest kernel threads seem to hang and show traces like
===
            INFO: task kworker/u2:0:9 blocked for more than 245 seconds.
            INFO: task (tmpfiles):482 blocked for more than 123 seconds.
            INFO: task (tmpfiles):482 blocked for more than 368 seconds.
            INFO: task systemd-random-:477 blocked for more than 368 seconds.
            [  492.932383]       Not tainted 6.6.7-100.fc37.x86_64 #1
            [  492.935404] "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
===

* I'm not yet sure how to fix this. I'd appreciate if you've suggestions.

Thank you.
---
  - Prasad