On 06/30/2009 12:08 PM, Korkakakis Nikos wrote:
Hi there all,
first of all I am writing a kernel module to handle some device using;
uname -a: Linux localhost 2.6.30-gentoo-r1 #1 SMP Sun Jun 28 02:52:23
EEST 2009 i686 AMD Phenom(tm) II X4 940 Processor AuthenticAMD GNU/Linux.
During the init phase of the module I allocate some memory via
kmalloc() in the following manner;
omm_dev_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL | GFP_DMA | GFP_ATOMIC);
GFP_KERNEL and GFP_ATOMIC are contradictory flags. Also, drivers should
generally not be using GFP_DMA, if the DMA mapping API is used this is
not needed.
I don't know if this is what is causing your problem or not.
if (!omm_dev_buffer) {
return -ENOMEM;
}
clear_buffer (omm_dev_buffer, PAGE_SIZE);
printk("omm_dev_init: kmalloc'ed omm_dev_buffer OK\n");
omm_messages = kmalloc(PAGE_SIZE, GFP_KERNEL | GFP_DMA);
printk ("dev_buff @ 0x%x messages @
0x%x\n",omm_dev_buffer,omm_messages);
if (!omm_messages) {
kfree(omm_dev_buffer); /* failing at this point means that the
other allocation succeeded */
return -ENOMEM;
}
clear_buffer (omm_messages, PAGE_SIZE);
where clear_buffer is just a wrapper for memset. My problem is that the
two consecutive memory allocation operations return the same memory
space (both pointers point the same address). If I change the malloc'ed
size ie PAGE_SIZE*2 then the process works as expected. kzalloc behaves
the same way, while alloc_page with the same flags(i.e.
alloc_page(GFP_KERNEL | GFP_DMA | GFP_ATOMIC) ) return a different
memory space and works as expected.
What am I missing here?
Thank's in advance :D
Nikos
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