Re: [PATCH] hw/scsi/lsi53c895a: add missing decrement of reentrancy counter

[Sven Schnelle <svens@stackframe.org>]

Thomas Huth <thuth@redhat.com> writes:

> On 28/01/2024 21.22, Sven Schnelle wrote:
>> When the maximum count of SCRIPTS instructions is reached, the code
>> stops execution and returns, but fails to decrement the reentrancy
>> counter. This effectively renders the SCSI controller unusable
>> because on next entry the reentrancy counter is still above the limit.
>> This bug was seen on HP-UX 10.20 which seems to trigger SCRIPTS
>> loops.
>
> Out of curiosity: What happened there before we introduced the
> reentrancy_level fix? Did it end up in an endless loop, or was it
> finishing at one point? In the latter case, we might need to adjust
> the "reentrancy_level > 8" to allow deeper nesting.

Without the reentrancy counter it was triggering the insn_processed
limit. The HP-UX scsi driver seems to spin on some memory value during
some SCSI writes (CDB with command 0x2a). So it is spinning in an
endless loop until the insn_processed counter will trigger the exit.
In HP-UX you will see a SCSI command timeout error in the kernel log
- at least i'm assuming that's related, but can't say for sure as
there's no kernel source available.