RE: Query regarding Kmemleak

Feb. 1, 2012

      ...
-----Original Message-----
From: kernelnewbies-bounces@kernelnewbies.org [mailto:kernelnewbies-
bounces@kernelnewbies.org] On Behalf Of Smital Desai
Sent: Tuesday, January 31, 2012 4:02 PM
To: Kernel Newbies
Subject: Query regarding Kmemleak
Hello ,
I am  just trying to understand Kmemleak support.
In a test program ,  allocating some memory using and vmalloc
() and
freeing it in exit () routine.
         But when i run a kmemleak , It reports this as a leak.
But isn't it a generic reuirement to allocate something for
the lifetime of
the module and free when we remove the module. ?   Can somebody
explain ?
I have provided the kmemleak output and my test program
below.
Thanks,
Smital Desai
==========================================================
=======================
cat  /sys/kernel/debug/memleak
unreferenced object 0xe1b18000 (size 512):
  comm "insmod", pid 1066, jiffies 4294953148 (age 54.630s)
  hex dump (first 32 bytes):
    36 1c 00 00 02 16 00 00 3c 1c 00 00 02 16 00 00  6.......<.......
    43 1c 00 00 02 16 00 00 4f 1c 00 00 02 16 00 00  C.......O.......
  backtrace:
    [<c0234ecc>] __vmalloc_node_range+0x1a8/0x1d0
    [<c0234f2c>] __vmalloc_node+0x38/0x44
    [<c023507c>] vmalloc+0x28/0x30
    [<bf00200c>] 0xbf00200c
    [<c0100458>] do_one_initcall+0x94/0x164
    [<c01d639c>] sys_init_module+0x70/0x190
    [<c0105d60>] ret_fast_syscall+0x0/0x30
    [<ffffffff>] 0xffffffff
unreferenced object 0xe1b1a000 (size 512):
  comm "insmod", pid 1066, jiffies 4294953148 (age 54.630s)
  hex dump (first 32 bytes):
    00 00 00 00 00 2c 00 00 00 00 00 00 2a 03 00 00  .....,......*...
    00 00 00 00 00 2c 00 00 bc 00 00 00 02 2e 00 00  .....,..........
  backtrace:
    [<c0234ecc>] __vmalloc_node_range+0x1a8/0x1d0
    [<c0234f2c>] __vmalloc_node+0x38/0x44
    [<c023507c>] vmalloc+0x28/0x30
    [<bf00201c>] 0xbf00201c
    [<c0100458>] do_one_initcall+0x94/0x164
    [<c01d639c>] sys_init_module+0x70/0x190
    [<c0105d60>] ret_fast_syscall+0x0/0x30
    [<ffffffff>] 0xffffffff
==========================================================
===========================
"test.c"
==========================================================
========================
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kmemleak.h>
char *ptr1, *ptr2;
/*
 * Some very simple testing. This function needs to be extended for
 * proper testing.
 */
static int __init kmemleak_test_init(void)
{
        ptr1 = vmalloc(512);
        ptr2 = vmalloc(512);
return 0;
}
module_init(kmemleak_test_init);
static void __exit kmemleak_test_exit(void)
{
       vfree(ptr1);
       vfree(ptr2);
}
module_exit(kmemleak_test_exit);
MODULE_LICENSE("GPL");
==========================================================
========================
Thanks and Regard
 Smital Desai
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Just to be clear:

Did you rmmod your module before doing the cat on
/sys/kernel/debug/memleak?

If not, I think the above output of memleak is what would be expected.

Jeff Haran