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On Sat, 28 Feb 2004 17:26:44 +0000 (GMT)
pankaj chauhan <chauhan_ait@yahoo.co.in> wrote:
>
>hi all ,
>
>i have a machine with 256Mb of RAM.
>
>i am using __get_free_pages{order 9} to get 2Mb memory
>( want it to be continous) in a module. i am accessing
>this memory in interrupt context..
>
>my system crashes down when i access this memory in
>interrupt context. during allocation i check that if
>__get_free_pages fails ( pointer returned is NULL) , i
>return an error.so i hope i am using memory in the
>interrupt context only if __get_free_pages succeeded.
>
>plz tell me what may be possible problem
Please take a look at this (grepping kernel source code is
always a good thing to do in such cases).
* The @flags argument may be one of:
*
* %GFP_USER - Allocate memory on behalf of user. May sleep.
*
* %GFP_KERNEL - Allocate normal kernel ram. May sleep.
*
* %GFP_ATOMIC - Allocation will not sleep. Use inside interrupt handlers.
*
* Additionally, the %GFP_DMA flag may be set to indicate the memory
* must be suitable for DMA. This can mean different things on different
* platforms. For example, on i386, it means that the memory must come
* from the first 16MB.
The possible problem is clearly how you try to allocate these
pages. If you're in interrupt context you CAN'T ask for these
with a flag GFP_KERNEL since it allows kmalloc() to sleep. And
if you try to sleep in interrupt context, you're searching for
havoc!
Regards.
- --
Angelo Dell'Aera 'buffer'
Antifork Research, Inc. http://buffer.antifork.org
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