From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755467Ab2HINdX (ORCPT ); Thu, 9 Aug 2012 09:33:23 -0400 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:43584 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754489Ab2HINdV (ORCPT ); Thu, 9 Aug 2012 09:33:21 -0400 Date: Thu, 9 Aug 2012 19:02:51 +0530 From: Srikar Dronamraju To: Oleg Nesterov Cc: Ingo Molnar , Peter Zijlstra , Ananth N Mavinakayanahalli , Anton Arapov , linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/7] uprobes: introduce MMF_HAS_UPROBES Message-ID: <20120809133251.GA26733@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20120808173659.GA13220@redhat.com> <20120808173747.GA13272@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20120808173747.GA13272@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) x-cbid: 12080913-6102-0000-0000-00000205E758 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Oleg Nesterov [2012-08-08 19:37:47]: > Add the new MMF_HAS_UPROBES flag. It is set by install_breakpoint() > and it is copied by dup_mmap(), uprobe_pre_sstep_notifier() checks > it to avoid the slow path if the task was never probed. Perhaps it > makes sense to check it in valid_vma(is_register => false) as well. > > This needs the new dup_mmap()->uprobe_dup_mmap() hook. We can't use > uprobe_reset_state() or put MMF_HAS_UPROBES into MMF_INIT_MASK, we > need oldmm->mmap_sem to avoid the race with uprobe_register() or > mmap() from another thread. > > Currently we never clear this bit, it can be false-positive after > uprobe_unregister() or uprobe_munmap() or if dup_mmap() hits the > probed VM_DONTCOPY vma. But this is fine correctness-wise and has > no effect unless the task hits the non-uprobe breakpoint. > In which case, cant we just delete uprobe_munmap() altogether. > Signed-off-by: Oleg Nesterov > --- > include/linux/sched.h | 2 ++ > include/linux/uprobes.h | 5 +++++ > kernel/events/uprobes.c | 22 +++++++++++++++++++++- > kernel/fork.c | 1 + > 4 files changed, 29 insertions(+), 1 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index cbf3a71..c0fcfb7 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -441,6 +441,8 @@ extern int get_dumpable(struct mm_struct *mm); > #define MMF_VM_HUGEPAGE 17 /* set when VM_HUGEPAGE is set on vma */ > #define MMF_EXE_FILE_CHANGED 18 /* see prctl_set_mm_exe_file() */ > > +#define MMF_HAS_UPROBES 19 /* might have uprobes */ > + > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK) > > struct sighand_struct { > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h > index 03ae547..4a37ab1 100644 > --- a/include/linux/uprobes.h > +++ b/include/linux/uprobes.h > @@ -108,6 +108,7 @@ extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_con > extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc); > extern int uprobe_mmap(struct vm_area_struct *vma); > extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end); > +extern void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm); > extern void uprobe_free_utask(struct task_struct *t); > extern void uprobe_copy_process(struct task_struct *t); > extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs); > @@ -138,6 +139,10 @@ static inline void > uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end) > { > } > +static inline void > +uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm) > +{ > +} > static inline void uprobe_notify_resume(struct pt_regs *regs) > { > } > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 309309e..2a42319 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -649,6 +649,7 @@ static int > install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, > struct vm_area_struct *vma, unsigned long vaddr) > { > + bool first_uprobe; > int ret; > > /* > @@ -680,7 +681,17 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, > uprobe->flags |= UPROBE_COPY_INSN; > } > > + /* > + * set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(), > + * the task can hit this breakpoint right after __replace_page(). > + */ > + first_uprobe = !test_bit(MMF_HAS_UPROBES, &mm->flags); > + if (first_uprobe) > + set_bit(MMF_HAS_UPROBES, &mm->flags); > + > ret = set_swbp(&uprobe->arch, mm, vaddr); > + if (ret && first_uprobe) > + clear_bit(MMF_HAS_UPROBES, &mm->flags); > > return ret; > } > @@ -1034,6 +1045,9 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon > if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */ > return; > > + if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags)) > + return; > + I am not sure whats the purpose of the above test > /* TODO: unmapping uprobe(s) will need more work */ and I am unable to think what more we would want to do here. > } > > @@ -1144,6 +1158,12 @@ void uprobe_reset_state(struct mm_struct *mm) > mm->uprobes_state.xol_area = NULL; > } > > +void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm) > +{ > + if (test_bit(MMF_HAS_UPROBES, &oldmm->flags)) > + set_bit(MMF_HAS_UPROBES, &newmm->flags); > +} > + > /* > * - search for a free slot. > */ > @@ -1511,7 +1531,7 @@ int uprobe_pre_sstep_notifier(struct pt_regs *regs) > { > struct uprobe_task *utask; > > - if (!current->mm) > + if (!current->mm || !test_bit(MMF_HAS_UPROBES, ¤t->mm->flags)) > return 0; > > utask = current->utask; > diff --git a/kernel/fork.c b/kernel/fork.c > index 0e419ab..ab970c3 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -350,6 +350,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm) > > down_write(&oldmm->mmap_sem); > flush_cache_dup_mm(oldmm); > + uprobe_dup_mmap(oldmm, mm); > /* > * Not linked in yet - no deadlock potential: > */ > -- > 1.5.5.1 >