netdev - Question about memory leak detector giving false positive report for net/core/flow.c

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Date:	Mon, 26 Sep 2011 23:17:24 +0800
From:	Huajun Li <huajun.li.lee@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>, linux-mm@...ck.org
Cc:	"\"Eric Dumaze\"t" <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	Huajun Li <huajun.li.lee@...il.com>
Subject: Question about memory leak detector giving false positive report for net/core/flow.c

Memory leak detector gives following memory leak report, it seems the
report is triggered by net/core/flow.c, but actually, it should be a
false positive report.
So, is there any idea from kmemleak side to fix/disable this false
positive report like this?
Yes, kmemleak_not_leak(...) could disable it, but is it suitable for this case ?

BTW, I wrote a simple test code to emulate net/core/flow.c behavior at
this stage which triggers the report, and it could also make kmemleak
give similar report, please check below test code:

kernel version:
#uname -a
Linux 3.1.0-rc7 #22 SMP Tue Sep 26 05:43:01 CST 2011 x86_64 x86_64
x86_64 GNU/Linux

memory leak report:
-------------------------------------------------------------------------------------------
unreferenced object 0xffff880073a70000 (size 8192):
  comm "swapper", pid 1, jiffies 4294937832 (age 445.740s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff8124db64>] create_object+0x144/0x360
    [<ffffffff8191192e>] kmemleak_alloc+0x7e/0x110
    [<ffffffff81235b26>] __kmalloc_node+0x156/0x3a0
    [<ffffffff81935512>] flow_cache_cpu_prepare.clone.1+0x58/0xc0
    [<ffffffff8214c361>] flow_cache_init_global+0xb6/0x1af
    [<ffffffff8100225d>] do_one_initcall+0x4d/0x260
    [<ffffffff820ec2e9>] kernel_init+0x161/0x23a
    [<ffffffff8194ab04>] kernel_thread_helper+0x4/0x10
    [<ffffffffffffffff>] 0xffffffffffffffff
unreferenced object 0xffff880073a74290 (size 8192):
  comm "swapper", pid 1, jiffies 4294937832 (age 445.740s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff8124db64>] create_object+0x144/0x360
    [<ffffffff8191192e>] kmemleak_alloc+0x7e/0x110
    [<ffffffff81235b26>] __kmalloc_node+0x156/0x3a0
    [<ffffffff81935512>] flow_cache_cpu_prepare.clone.1+0x58/0xc0
    [<ffffffff8214c361>] flow_cache_init_global+0xb6/0x1af
    [<ffffffff8100225d>] do_one_initcall+0x4d/0x260
    [<ffffffff820ec2e9>] kernel_init+0x161/0x23a
    [<ffffffff8194ab04>] kernel_thread_helper+0x4/0x10
    [<ffffffffffffffff>] 0xffffffffffffffff



Simple test code to reproduce a similar report:
-----------------------------------------------------------------------------------------
MODULE_LICENSE("GPL");

struct test {
        int *pt;
};

static struct test __percpu *percpu;

static int __init test_init(void)
{
        int i;

        percpu = alloc_percpu(struct test);
        if (!percpu)
                return -ENOMEM;

        for_each_online_cpu(i) {
                struct test *p = per_cpu_ptr(percpu, i);
                p->pt = kmalloc(sizeof(int), GFP_KERNEL);
        }

        return 0;
}

static void __exit test_exit(void)
{
        int i;

        for_each_possible_cpu(i) {
                struct test *p = per_cpu_ptr(percpu, i);
                if (p->pt)
                        kfree(p->pt);
        }

        if (percpu)
                free_percpu(percpu);
}
module_init(test_init);
module_exit(test_exit);
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