kmalloc() of 4MB causes "kernel BUG at slab.c:1542!"

[please cc me on any responses]

Environment: 2.4.0 released, Pentium III with 256MB's of RAM.
Problem: kmalloc() of 4M causes kernel message "kernel BUG at slab.c:1542"

Here is the dmesg output:

kernel BUG at slab.c:1542!

invalid operand: 0000
CPU:    0
EIP:    0010:[<c0129b84>]
EFLAGS: 00010282
eax: 0000001b   ebx: d2922000   ecx: cdf6c000   edx: 00000000
esi: 00000007   edi: 00000000   ebp: 0806f124   esp: cb1bdef4
ds: 0018   es: 0018   ss: 0018
Process insmod (pid: 24167, stackpage=cb1bd000)
Stack: c02148eb c021498b 00000606 00000286 00000001 c02a75ec 00000029 d2922000 
       00000000 d2922083 01000000 00000007 d29221c0 01000000 c0116c65 00000000 
       cc8a6000 0000020c cc8a7000 00000060 ffffffea 00000003 c2be5420 00000060 
Call Trace: [<d2922000>] [<d2922083>] [<d29221c0>] [<c0116c65>] [<d2920000>] [<d2922060>] [<c0109057>] 

Code: 0f 0b 83 c4 0c 31 c0 83 c4 10 5b 5e c3 eb 0d 90 90 90 90 90 

Repeat by:

	Compile simple driver attached.
	$ insmod test.o Amt=4096

Rick Richardson  [email protected]  http://home.mn.rr.com/richardsons/
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#include <linux/config.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/config.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/errno.h>
#include <linux/in.h>
#include <linux/mm.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/if_arp.h>
#include <linux/skbuff.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/init.h>

static size_t Amt = 1;
MODULE_PARM(Amt, "l");
MODULE_PARM_DESC(Amt, "Pages of memory to allocate");

static void *mem;

static int __init
init(void)

{
        /* Announce this module has been loaded. */
        printk(KERN_INFO "test loading; allocate %d bytes\n", Amt*4096);

        mem = kmalloc(Amt*4096, GFP_KERNEL);
        if (!mem) return (-ENOMEM);

        printk(KERN_INFO "test loaded\n");
        return 0;
}

static void __exit
fini(void)

{
        printk(KERN_INFO "test unloading\n");
        kfree(mem);
}

module_init(init);
module_exit(fini);

The most you can kmalloc() is 128KB unless this has changed in the 2.4 kernel which I doubt. If you want a region of memory that large, use vmalloc(). Of course, this doesn't guarantee a contiguous region.

BAPper
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** Reply to message from Brian Pomerantz <[email protected]> on Wed, 17 Jan 2001 12:17:19 -0800

Couldn't you also use get_free_pages (commonly abbreviated as "gfp")? You can alloc up to 2MB chunks on an x86 I think.

Timur Tabi - [email protected]
Interactive Silicon - http://www.interactivesi.com

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This BUG() has been been removed in the later -ac patches as it was meant to be a temporary debugging help during the -test3 slab.c changes. This does not however remove the constraint that kmalloc can only allocate a maximum of 128KB. How you solve this will depend what you want to use the memory for.

-- Hans

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