linux-kernel - Re: [PATCH v3] kernel/signal: Signal-based pre-coredump notification

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Date:   Wed, 24 Oct 2018 16:02:15 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Enke Chen <enkechen@...co.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian@...uner.io>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Roman Gushchin <guro@...com>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        "Victor Kamensky (kamensky)" <kamensky@...co.com>,
        xe-linux-external@...co.com, Stefan Strogin <sstrogin@...co.com>
Subject: Re: [PATCH v3] kernel/signal: Signal-based pre-coredump notification

On 10/23, Enke Chen wrote:
>
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -590,6 +590,12 @@ void do_coredump(const kernel_siginfo_t *siginfo)
>  	if (retval < 0)
>  		goto fail_creds;
>
> +	/*
> +	 * Send the pre-coredump signal to the parent if requested.
> +	 */
> +	do_notify_parent_predump();
> +	cond_resched();

I am still not sure cond_resched() makes any sense here...

> @@ -1553,6 +1553,9 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
>  	tty_audit_fork(sig);
>  	sched_autogroup_fork(sig);
>
> +	/* Clear the pre-coredump signal for the child */
> +	sig->predump_signal = 0;

No need, copy_signal() does zalloc().


> +void do_notify_parent_predump(void)
> +{
> +	struct sighand_struct *sighand;
> +	struct kernel_siginfo info;
> +	struct task_struct *parent;
> +	unsigned long flags;
> +	int sig;
> +
> +	read_lock(&tasklist_lock);
> +	parent = current->parent;
> +	sig = parent->signal->predump_signal;
> +	if (sig != 0) {
> +		clear_siginfo(&info);
> +		info.si_pid = task_tgid_vnr(current);
> +		info.si_signo = sig;
> +		if (sig == SIGCHLD)
> +			info.si_code = CLD_PREDUMP;
> +
> +		sighand = parent->sighand;
> +		spin_lock_irqsave(&sighand->siglock, flags);
> +		__group_send_sig_info(sig, &info, parent);
> +		spin_unlock_irqrestore(&sighand->siglock, flags);

You can just use do_send_sig_info() and remove sighand/flags/spin_lock_irqsave.

Perhaps the "likely" predump_signal==0 check at the start makes sense to avoid
read_lock(tasklist).

And I'd suggest to move it into coredump.c and make it static. It won't have
another user.

Oleg.