linux-kernel - Re: [PATCH v2 7/9] trace_uprobe/sdt: Fix multiple update of same reference counter

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Date:   Mon, 9 Apr 2018 15:29:28 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     mhiramat@...nel.org, peterz@...radead.org,
        srikar@...ux.vnet.ibm.com, rostedt@...dmis.org, acme@...nel.org,
        ananth@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        alexander.shishkin@...ux.intel.com, alexis.berlemont@...il.com,
        corbet@....net, dan.j.williams@...el.com, jolsa@...hat.com,
        kan.liang@...el.com, kjlx@...pleofstupid.com,
        kstewart@...uxfoundation.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        milian.wolff@...b.com, mingo@...hat.com, namhyung@...nel.org,
        naveen.n.rao@...ux.vnet.ibm.com, pc@...ibm.com, tglx@...utronix.de,
        yao.jin@...ux.intel.com, fengguang.wu@...el.com, jglisse@...hat.com
Subject: Re: [PATCH v2 7/9] trace_uprobe/sdt: Fix multiple update of same
 reference counter

On 04/04, Ravi Bangoria wrote:
>
> +static void sdt_add_mm_list(struct trace_uprobe *tu, struct mm_struct *mm)
> +{
> +	struct mmu_notifier *mn;
> +	struct sdt_mm_list *sml = kzalloc(sizeof(*sml), GFP_KERNEL);
> +
> +	if (!sml)
> +		return;
> +	sml->mm = mm;
> +	list_add(&(sml->list), &(tu->sml.list));
> +
> +	/* Register mmu_notifier for this mm. */
> +	mn = kzalloc(sizeof(*mn), GFP_KERNEL);
> +	if (!mn)
> +		return;
> +
> +	mn->ops = &sdt_mmu_notifier_ops;
> +	__mmu_notifier_register(mn, mm);
> +}

and what if __mmu_notifier_register() fails simply because signal_pending() == T?
see mm_take_all_locks().

at first glance this all look suspicious and sub-optimal, but let me repeat that
I didn't read this version yet.

Oleg.