Re: [PATCH 4/7] uprobes: Do not play with utask in xol_get_insn_slot()

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Oleg Nesterov <oleg@redhat.com> [2012-12-31 18:52:23]:

> pre_ssout()->xol_get_insn_slot() path is confusing and buggy. This patch
> cleanups the code, the next one fixes the bug.
> 
> Change xol_get_insn_slot() to only allocate the slot and do nothing more,
> move the initialization of utask->xol_vaddr/vaddr into pre_ssout().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  kernel/events/uprobes.c |   37 +++++++++++++++++++++----------------
>  1 files changed, 21 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index b09b3ba..2ed6239 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1176,30 +1176,26 @@ static unsigned long xol_take_insn_slot(struct xol_area *area)
>  }
> 
>  /*
> - * xol_get_insn_slot - If was not allocated a slot, then
> - * allocate a slot.
> + * xol_get_insn_slot - allocate a slot for xol.
>   * Returns the allocated slot address or 0.
>   */
> -static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot_addr)
> +static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
>  {
>  	struct xol_area *area;
>  	unsigned long offset;
> +	unsigned long xol_vaddr;
>  	void *vaddr;
> 
>  	area = get_xol_area();
>  	if (!area)
>  		return 0;
> 
> -	current->utask->xol_vaddr = xol_take_insn_slot(area);
> -	/*
> -	 * Initialize the slot if xol_vaddr points to valid
> -	 * instruction slot.
> -	 */
> -	if (unlikely(!current->utask->xol_vaddr))
> +	xol_vaddr = xol_take_insn_slot(area);
> +	if (unlikely(!xol_vaddr))
>  		return 0;
> 
> -	current->utask->vaddr = slot_addr;
> -	offset = current->utask->xol_vaddr & ~PAGE_MASK;
> +	/* Initialize the slot */
> +	offset = xol_vaddr & ~PAGE_MASK;
>  	vaddr = kmap_atomic(area->page);
>  	memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
>  	kunmap_atomic(vaddr);
> @@ -1209,7 +1205,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot
>  	 */
>  	flush_dcache_page(area->page);
> 
> -	return current->utask->xol_vaddr;
> +	return xol_vaddr;
>  }
> 
>  /*
> @@ -1306,12 +1302,21 @@ static struct uprobe_task *get_utask(void)
> 
>  /* Prepare to single-step probed instruction out of line. */
>  static int
> -pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long vaddr)
> +pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
>  {
> -	if (xol_get_insn_slot(uprobe, vaddr) && !arch_uprobe_pre_xol(&uprobe->arch, regs))
> -		return 0;
> +	struct uprobe_task *utask;
> +	unsigned long xol_vaddr;
> +
> +	utask = current->utask;
> +
> +	xol_vaddr = xol_get_insn_slot(uprobe);
> +	if (!xol_vaddr)
> +		return -ENOMEM;
> +
> +	utask->xol_vaddr = xol_vaddr;
> +	utask->vaddr = bp_vaddr;
> 
> -	return -EFAULT;
> +	return arch_uprobe_pre_xol(&uprobe->arch, regs);
>  }
> 
>  /*
> -- 
> 1.5.5.1
>