linux-kernel - Re: kmemleak splat on copy

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Message-ID: <20170206094741.GB3097@dhcp22.suse.cz>
Date:   Mon, 6 Feb 2017 10:47:41 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: kmemleak splat on copy_process()

On Fri 03-02-17 13:06:04, Luis R. Rodriguez wrote:
> On next-20170125 running some kselftest not yet upstream I eventually
> get a kmemleak splat:
> 
> unreferenced object 0xffffa7b1034b4000 (size 16384):
>   comm "driver_data.sh", pid 6506, jiffies 4295068366 (age 1697.272s)
>   hex dump (first 32 bytes):
>     9d 6e ac 57 00 00 00 00 74 2d 64 72 69 76 65 72  .n.W....t-driver
>     5f 64 61 74 61 2e 62 69 6e 0a 00 00 00 00 00 00  _data.bin.......
>   backtrace:
>     [<ffffffff9005f7fa>] kmemleak_alloc+0x4a/0xa0
>     [<ffffffff8fbe7006>] __vmalloc_node_range+0x206/0x2a0
>     [<ffffffff8fa7f3e9>] copy_process.part.36+0x609/0x1cc0
>     [<ffffffff8fa80c77>] _do_fork+0xd7/0x390
>     [<ffffffff8fa80fd9>] SyS_clone+0x19/0x20
>     [<ffffffff8fa03b4b>] do_syscall_64+0x5b/0xc0
>     [<ffffffff9006b3af>] return_from_SYSCALL_64+0x0/0x6a
>     [<ffffffffffffffff>] 0xffffffffffffffff
> 
> As per gdb:
> 
> (gdb) l *(copy_process+0x609)
> 0xffffffff8107f3e9 is in copy_process (kernel/fork.c:204).
> warning: Source file is more recent than executable.
> 199             /*
> 200              * We can't call find_vm_area() in interrupt context, and
> 201              * free_thread_stack() can be called in interrupt context,
> 202              * so cache the vm_struct.
> 203              */
> 204             if (stack) {
> 205                     tsk->stack_vm_area = find_vm_area(stack);
> 206             }
> 207             return stack;
> 208     #else

Could you check the state of the above process (pid 6506)? Does it still
own its stack? From a quick check I do not see any leak there either.
-- 
Michal Hocko
SUSE Labs