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Date: Mon, 10 Jul 2006 06:46:57 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: David Howells <dhowells@redhat.com>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH 7/8] FDPIC: Add coredump capability for the ELF-FDPIC binfmt [try #4]
Message-ID: <20060710024657.GA255@oleg>
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David Howells wrote:
>
> +static int elf_fdpic_core_dump(long signr, struct pt_regs *regs,
> +			       struct file *file)
> +{
>
>  [... snip ...]
>
> +		read_lock(&tasklist_lock);
> +		do_each_thread(g,p)
> +			if (current->mm == p->mm && current != p) {
> +				tmp = kzalloc(sizeof(*tmp), GFP_ATOMIC);
> +				if (!tmp) {
> +					read_unlock(&tasklist_lock);
> +					goto cleanup;
> +				}
> +				INIT_LIST_HEAD(&tmp->list);
> +				tmp->thread = p;
> +				list_add(&tmp->list, &thread_list);
> +			}
> +		while_each_thread(g,p);
> +		read_unlock(&tasklist_lock);

Do you see any reason for tasklist_lock here (and in elf_core_dump) ?

do_each_thread() is rcu-safe, and all tasks which use this ->mm must
sleep in wait_for_completion(&mm->core_done) at this point.

Oleg.