Commit 806a98bd authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes: Rationalize the usage of filter_chain() 



filter_chain() was added into install_breakpoint/remove_breakpoint to
simplify the initial changes but this is sub-optimal.

This patch shifts the callsite to the callers, register_for_each_vma()
and uprobe_mmap(). This way:

- It will be easier to add the new arguments. This is the main reason,
  we can do more optimizations later.

- register_for_each_vma(is_register => true) can be optimized, we only
  need to consult the new consumer. The previous consumers were already
  asked when they called uprobe_register().

This patch also moves the MMF_HAS_UPROBES check from remove_breakpoint(),
this allows to avoid the potentionally costly filter_chain(). Note that
register_for_each_vma(is_register => false) doesn't really need to take
->consumer_rwsem, but I don't think it makes sense to optimize this and
introduce filter_chain_lockless().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 66d06dff

kernel/events/uprobes.c

+21 −23
Original line number Diff line number Diff line
@@ -579,6 +579,11 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file, 
	return ret;

}



static inline bool consumer_filter(struct uprobe_consumer *uc)

{

	return true; /* TODO: !uc->filter || uc->filter(...) */

}



static bool filter_chain(struct uprobe *uprobe)

{

	struct uprobe_consumer *uc;
@@ -586,8 +591,7 @@ static bool filter_chain(struct uprobe *uprobe) 


	down_read(&uprobe->consumer_rwsem);

	for (uc = uprobe->consumers; uc; uc = uc->next) {

		/* TODO: ret = uc->filter(...) */

		ret = true;

		ret = consumer_filter(uc);

		if (ret)

			break;

	}
@@ -603,15 +607,6 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, 
	bool first_uprobe;

	int ret;



	/*

	 * If probe is being deleted, unregister thread could be done with

	 * the vma-rmap-walk through. Adding a probe now can be fatal since

	 * nobody will be able to cleanup. But in this case filter_chain()

	 * must return false, all consumers have gone away.

	 */

	if (!filter_chain(uprobe))

		return 0;



	ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);

	if (ret)

		return ret;
@@ -636,12 +631,6 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, 
static int

remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)

{

	if (!test_bit(MMF_HAS_UPROBES, &mm->flags))

		return 0;



	if (filter_chain(uprobe))

		return 0;



	set_bit(MMF_RECALC_UPROBES, &mm->flags);

	return set_orig_insn(&uprobe->arch, mm, vaddr);

}
@@ -781,10 +770,14 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register) 
		    vaddr_to_offset(vma, info->vaddr) != uprobe->offset)

			goto unlock;



		if (is_register)

		if (is_register) {

			/* consult only the "caller", new consumer. */

			if (consumer_filter(uprobe->consumers))

				err = install_breakpoint(uprobe, mm, vma, info->vaddr);

		else

		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {

			if (!filter_chain(uprobe))

				err |= remove_breakpoint(uprobe, mm, info->vaddr);

		}



 unlock:

		up_write(&mm->mmap_sem);
@@ -968,9 +961,14 @@ int uprobe_mmap(struct vm_area_struct *vma) 


	mutex_lock(uprobes_mmap_hash(inode));

	build_probe_list(inode, vma, vma->vm_start, vma->vm_end, &tmp_list);



	/*

	 * We can race with uprobe_unregister(), this uprobe can be already

	 * removed. But in this case filter_chain() must return false, all

	 * consumers have gone away.

	 */

	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {

		if (!fatal_signal_pending(current)) {

		if (!fatal_signal_pending(current) &&

		    filter_chain(uprobe)) {

			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);

			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);

		}

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