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Violators will be prosecuted for from ; Wed, 22 Aug 2018 16:07:27 +0100 Date: Wed, 22 Aug 2018 08:07:18 -0700 From: Srikar Dronamraju Subject: Re: [RFC v8 PATCH 2/5] uprobes: introduce has_uprobes helper Reply-To: Srikar Dronamraju References: <1534358990-85530-1-git-send-email-yang.shi@linux.alibaba.com> <1534358990-85530-3-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: Message-Id: <20180822150718.GB52756@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: 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, linux-mm@kvack.org, Oleg Nesterov , liu.song.a23@gmail.com, ravi.bangoria@linux.ibm.com, linux-kernel@vger.kernel.org * Vlastimil Babka [2018-08-22 12:55:59]: > 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... I too feel the name is not apt. Can you make this vma_has_uprobes and convert the current vma_has_uprobes to __vma_has_uprobes? > > > { > > 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. That is a very good observation. One think we can probably do is pass an extra parameter to has_uprobes(), depending on which we should skip this check. such that when we call from uprobes_munmap(), we continue as is but when calling from do_munmap_zap_rlock(), we skip the check. > > > - 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); > > } -- Thanks and Regards Srikar Dronamraju