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Re: [Qemu-block] Limiting coroutine stack usage

From: John Snow
Subject: Re: [Qemu-block] Limiting coroutine stack usage
Date: Thu, 22 Feb 2018 12:06:44 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 02/22/2018 05:57 AM, Kevin Wolf wrote:
> Am 20.02.2018 um 22:54 hat Paolo Bonzini geschrieben:
>> On 20/02/2018 18:04, Peter Lieven wrote:
>>> Hi,
>>> I remember we discussed a long time ago to limit the stack usage of all
>>> functions that are executed in a coroutine
>>> context to a very low value to be able to safely limit the coroutine
>>> stack size as well.
>> IIRC the only issue was that hw/ide/atapi.c has mutual recursion between
>> ide_atapi_cmd_reply_end -> ide_transfer_start -> ahci_start_transfer ->
>> ide_atapi_cmd_reply_end.
>> But perhaps it's not an issue, somebody needs to audit the code.
> I think John intended to get rid of the recursion sometime, but I doubt
> he has had the time so far.

It hasn't been a priority for me.

Paolo tried to fix ATAPI by adding a BH callback, but that added the
possibility of a migration halfway through a data transfer IIRC.

If anyone wants to tackle it, I'll dig up Paolo's patches.


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