linux-kernel - Re: [PATCH v2 2/4] coredump: ensure the fpu state is flushed for proper multi-threaded core dump

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Message-ID: <20120511165128.GA21511@redhat.com>
Date:	Fri, 11 May 2012 18:51:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	torvalds@...ux-foundation.org, hpa@...or.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, suresh@...stanetworks.com
Subject: Re: [PATCH v2 2/4] coredump: ensure the fpu state is flushed for
	proper multi-threaded core dump

On 05/10, Suresh Siddha wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1930,8 +1930,21 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
>  		core_waiters = zap_threads(tsk, mm, core_state, exit_code);
>  	up_write(&mm->mmap_sem);
>
> -	if (core_waiters > 0)
> +	if (core_waiters > 0) {
> +		struct core_thread *ptr;
> +
>  		wait_for_completion(&core_state->startup);
> +		/*
> +		 * Wait for all the threads to become inactive, so that
> +		 * all the thread context (extended register state, like
> +		 * fpu etc) gets copied to the memory.
> +		 */
> +		ptr = core_state->dumper.next;
> +		while (ptr != NULL) {
> +			wait_task_inactive(ptr->task, 0);
> +			ptr = ptr->next;
> +		}
> +	}

OK, but this adds the unnecessary penalty if we are not going to dump
the core.

Perhaps it makes sense to create a separate helper and call it from
do_coredump() right before "retval = binfmt->core_dump(&cprm)" ?

This also increases the chance that wait_task_inactive() won't actually
wait.

Oleg.

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