From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) by kanga.kvack.org (Postfix) with ESMTP id 98BF46B23F7 for ; Wed, 22 Aug 2018 06:56:03 -0400 (EDT) Received: by mail-pg1-f197.google.com with SMTP id v195-v6so910102pgb.0 for ; Wed, 22 Aug 2018 03:56:03 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d127-v6si1573771pfa.189.2018.08.22.03.56.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 Aug 2018 03:56:02 -0700 (PDT) Subject: Re: [RFC v8 PATCH 2/5] uprobes: introduce has_uprobes helper References: <1534358990-85530-1-git-send-email-yang.shi@linux.alibaba.com> <1534358990-85530-3-git-send-email-yang.shi@linux.alibaba.com> From: Vlastimil Babka Message-ID: Date: Wed, 22 Aug 2018 12:55:59 +0200 MIME-Version: 1.0 In-Reply-To: <1534358990-85530-3-git-send-email-yang.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi , mhocko@kernel.org, willy@infradead.org, ldufour@linux.vnet.ibm.com, kirill@shutemov.name, akpm@linux-foundation.org, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org On 08/15/2018 08:49 PM, Yang Shi wrote: > We need check if mm or vma has uprobes in the following patch to check > if a vma could be unmapped with holding read mmap_sem. The checks and > pre-conditions used by uprobe_munmap() look just suitable for this > purpose. > > Extracting those checks into a helper function, has_uprobes(). > > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Arnaldo Carvalho de Melo > Cc: Alexander Shishkin > Cc: Jiri Olsa > Cc: Namhyung Kim > Cc: Vlastimil Babka > Signed-off-by: Yang Shi > --- > include/linux/uprobes.h | 7 +++++++ > kernel/events/uprobes.c | 23 ++++++++++++++++------- > 2 files changed, 23 insertions(+), 7 deletions(-) > > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h > index 0a294e9..418764e 100644 > --- a/include/linux/uprobes.h > +++ b/include/linux/uprobes.h > @@ -149,6 +149,8 @@ struct uprobes_state { > extern bool arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs); > extern void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr, > void *src, unsigned long len); > +extern bool has_uprobes(struct vm_area_struct *vma, unsigned long start, > + unsigned long end); > #else /* !CONFIG_UPROBES */ > struct uprobes_state { > }; > @@ -203,5 +205,10 @@ static inline void uprobe_copy_process(struct task_struct *t, unsigned long flag > static inline void uprobe_clear_state(struct mm_struct *mm) > { > } > +static inline bool has_uprobes(struct vm_area_struct *vma, unsigned long start, > + unsgined long end) > +{ > + return false; > +} > #endif /* !CONFIG_UPROBES */ > #endif /* _LINUX_UPROBES_H */ > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index aed1ba5..568481c 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -1114,22 +1114,31 @@ int uprobe_mmap(struct vm_area_struct *vma) > return !!n; > } > > -/* > - * Called in context of a munmap of a vma. > - */ > -void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end) > +bool > +has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long end) The name is not really great... > { > if (no_uprobe_events() || !valid_vma(vma, false)) > - return; > + return false; > > if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */ > - return; > + return false; > > if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags) || > test_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags)) This means that vma might have uprobes, but since RECALC is already set, we don't need to set it again. That's different from "has uprobes". Perhaps something like vma_needs_recalc_uprobes() ? But I also worry there might be a race where we initially return false because of MMF_RECALC_UPROBES, then the flag is cleared while vma's still have uprobes, then we downgrade mmap_sem and skip uprobe_munmap(). Should be checked if e.g. mmap_sem and vma visibility changes protects this case from happening. > - return; > + return false; > > if (vma_has_uprobes(vma, start, end)) > + return true; > + > + return false; Simpler: return vma_has_uprobes(vma, start, end); > +} > + > +/* > + * Called in context of a munmap of a vma. > + */ > +void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end) > +{ > + if (has_uprobes(vma, start, end)) > set_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags); > } > >