linux-kernel - Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference count (semaphore)

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Date:   Mon, 23 Jul 2018 18:26:29 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     srikar@...ux.vnet.ibm.com, rostedt@...dmis.org,
        mhiramat@...nel.org, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org,
        linux-kernel@...r.kernel.org, ananth@...ux.vnet.ibm.com,
        alexis.berlemont@...il.com, naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com
Subject: Re: [PATCH v6 3/6] Uprobes: Support SDT markers having reference
 count (semaphore)

I have a mixed feeling about this series... I'll try to summarise my thinking
tomorrow, but I do not see any obvious problem so far. Although I have some
concerns about 5/6, I need to re-read it after sleep.


On 07/16, Ravi Bangoria wrote:
>
> +static int delayed_uprobe_install(struct vm_area_struct *vma)
> +{
> +	struct list_head *pos, *q;
> +	struct delayed_uprobe *du;
> +	unsigned long vaddr;
> +	int ret = 0, err = 0;
> +
> +	mutex_lock(&delayed_uprobe_lock);
> +	list_for_each_safe(pos, q, &delayed_uprobe_list) {
> +		du = list_entry(pos, struct delayed_uprobe, list);
> +
> +		if (!du->uprobe->ref_ctr_offset ||

Is it possible to see ->ref_ctr_offset == 0 in delayed_uprobe_list?

> @@ -1072,7 +1282,13 @@ int uprobe_mmap(struct vm_area_struct *vma)
>  	struct uprobe *uprobe, *u;
>  	struct inode *inode;
>  
> -	if (no_uprobe_events() || !valid_vma(vma, true))
> +	if (no_uprobe_events())
> +		return 0;
> +
> +	if (vma->vm_flags & VM_WRITE)
> +		delayed_uprobe_install(vma);

Obviously not nice performance-wise... OK, I do not know if it will actually
hurt in practice and probably we can use the better data structures if necessary.
But can't we check MMF_HAS_UPROBES at least? I mean,

	if (vma->vm_flags & VM_WRITE && test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
		delayed_uprobe_install(vma);

?


Perhaps we can even add another flag later, MMF_HAS_DELAYED_UPROBES set by
delayed_uprobe_add().

Oleg.