Re: [Patch 0/2] iscsit/isert deadlock prevention under heavy I/O

[David Jeffery <djeffery@redhat.com>]

On Sun, Mar 13, 2022 at 5:59 AM Max Gurtovoy <mgurtovoy@nvidia.com> wrote:
>
> Hi David,
>
> thanks for the report.
>
> Please check how we fixed that in NVMf in Sagi's commit:
>
> nvmet-rdma: fix possible bogus dereference under heavy load (commit:
> 8407879c4e0d77)
>
> Maybe this can be done in isert and will solve this problem in a simpler
> way.
>
> is it necessary to change max_cmd_sn ?
>
>

Hello,

Sure, there are alternative methods which could fix this immediate
issue. e.g. We could make the command structs for scsi commands get
allocated from a mempool. Is there a particular reason you don't want
to do anything to modify max_cmd_sn behavior?

I didn't do something like this as it seems to me to go against the
intent of the design. It makes the iscsi window mostly meaningless in
some conditions and complicates any allocation path since it now must
gracefully and sanely handle an iscsi_cmd/isert_cmd not existing. I
assume special commands like task-management, logouts, and pings would
need a separate allocation source to keep from being dropped under
memory load.

David Jeffery