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From: Evgeny Yakovlev <eyakovlev@virtuozzo.com>
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Date: Wed, 29 Jun 2016 11:35:04 +0300
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Subject: Re: [Qemu-devel] [PATCH 2/3] ide: ignore retry_unit check for
 non-retry operations
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To: Paolo Bonzini <pbonzini@redhat.com>, "Denis V. Lunev" <den@openvz.org>, qemu-block@nongnu.org, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, John Snow <jsnow@redhat.com>



On 28.06.2016 23:56, Paolo Bonzini wrote:
>
> On 24/06/2016 17:06, Denis V. Lunev wrote:
>> When doing DMA request ide/core.c will set s->retry_unit to s->unit in
>> ide_start_dma. When dma completes ide_set_inactive sets retry_unit to -1.
>> After that ide_flush_cache runs and fails thanks to blkdebug.
>> ide_flush_cb calls ide_handle_rw_error which asserts that s->retry_unit
>> == s->unit. But s->retry_unit is still -1 after previous DMA completion
>> and flush does not use anything related to retry.
> Wouldn't the assertion fail for a PIO read/write too?  Perhaps
> retry_unit should be set to s->unit in ide_transfer_start too.

If PIO follows DMA and fails then yes, it looks like it will trigger an 
assert. I am not sure about setting retry_unit in ide_transfer_start. It 
looks like currently only DMA I/O entries touch retry_unit at all. Does 
that mean that PIO, flush, etc do not support retries by design and we 
need to add more exceptions to assert check or is it a real bug in how 
retries are initialized?

>
> Paolo