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Re: [Qemu-block] Limiting coroutine stack usage

From: Peter Lieven
Subject: Re: [Qemu-block] Limiting coroutine stack usage
Date: Thu, 22 Feb 2018 12:42:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

Am 22.02.2018 um 12:32 schrieb Kevin Wolf:
> Am 22.02.2018 um 12:01 hat Peter Lieven geschrieben:
>> Am 22.02.2018 um 11:57 schrieb Kevin Wolf:
>>> 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.
>> Apart from this is is possible to define special cflags in the
>> Makefile.objs just for a subdirectory? I have patches ready to make
>> the block layer files and other coroutine users compile with
>> -Wstack-size=2048. But I do not want to specify each file separately.
> Our Makefiles have lines like this:
>     iscsi.o-cflags     := $(LIBISCSI_CFLAGS)
> I don't think there is a direct mechanism to apply cflags to a whole
> directory or just to block-obj-y/block-obj-m, but just looping over them
> could work. I'm not a Makefile expert at all, but after some toying with
> a simple example, something like this might work:
>     $(foreach x,$(block-obj-y),$(eval $x-cflags += -Wstack-size=2048))

Thanks for the hint.

If noone comes up with a better idea I will try this.


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