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Message-ID: <20130103115613.GD8140@linux.vnet.ibm.com>
Date: Thu, 3 Jan 2013 17:26:13 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Anton Arapov <anton@...hat.com>,
Frank Eigler <fche@...hat.com>,
Josh Stone <jistone@...hat.com>,
"Suzuki K. Poulose" <suzuki@...ibm.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] uprobes: Rationalize the usage of filter_chain()
* Oleg Nesterov <oleg@...hat.com> [2012-12-28 19:13:10]:
> 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: Oleg Nesterov <oleg@...hat.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> ---
> kernel/events/uprobes.c | 44 +++++++++++++++++++++-----------------------
> 1 files changed, 21 insertions(+), 23 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 105ac0d..60b0a90 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -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)
> - err = install_breakpoint(uprobe, mm, vma, info->vaddr);
> - else
> - err |= remove_breakpoint(uprobe, mm, info->vaddr);
> + if (is_register) {
> + /* consult only the "caller", new consumer. */
> + if (consumer_filter(uprobe->consumers))
> + err = install_breakpoint(uprobe, mm, vma, info->vaddr);
> + } 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);
> }
> --
> 1.5.5.1
>
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