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Date: Thu, 31 Mar 2016 15:15:34 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Jiri Slaby <jslaby@suse.cz>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/4] fork: free thread in copy_process on failure
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On Thu, 31 Mar 2016 09:55:55 +0200 Jiri Slaby <jslaby@suse.cz> wrote:

> When using this program (as root):
>
> ...
>
> 		ret = ioperm(10, 20, 0);

ah-hah.

> 		if (ret < 0)
> 			err(1, "ioperm");
> 
> 		for (a = 0; a < ITER; a++)
> 			run_forkers();
> 
> 		return 0;
> 	}
> 
> kmemleak reports many occurences of this leak:
> unreferenced object 0xffff8805917c8000 (size 8192):
>   comm "fork-leak", pid 2932, jiffies 4295354292 (age 1871.028s)
>   hex dump (first 32 bytes):
>     ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
>     ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
>   backtrace:
>     [<ffffffff814cfbf5>] kmemdup+0x25/0x50
>     [<ffffffff8103ab43>] copy_thread_tls+0x6c3/0x9a0
>     [<ffffffff81150174>] copy_process+0x1a84/0x5790
>     [<ffffffff811dc375>] wake_up_new_task+0x2d5/0x6f0
>     [<ffffffff8115411d>] _do_fork+0x12d/0x820
> ...

The missing info here is "due to the leakage of the memory which should
have been freed in arch/x86/kernel/process.c:exit_thread().