[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Fri, 9 Sep 2022 09:10:08 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Laurent Dufour <ldufour@...ux.ibm.com>
Cc: akpm@...ux-foundation.org, michel@...pinasse.org,
jglisse@...gle.com, mhocko@...e.com, vbabka@...e.cz,
hannes@...xchg.org, mgorman@...e.de, dave@...olabs.net,
willy@...radead.org, liam.howlett@...cle.com, peterz@...radead.org,
laurent.dufour@...ibm.com, paulmck@...nel.org, luto@...nel.org,
songliubraving@...com, peterx@...hat.com, david@...hat.com,
dhowells@...hat.com, hughd@...gle.com, bigeasy@...utronix.de,
kent.overstreet@...ux.dev, rientjes@...gle.com,
axelrasmussen@...gle.com, joelaf@...gle.com, minchan@...gle.com,
kernel-team@...roid.com, linux-mm@...ck.org,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND 21/28] mm: introduce find_and_lock_anon_vma to
be used from arch-specific code
On Fri, Sep 9, 2022 at 7:38 AM Laurent Dufour <ldufour@...ux.ibm.com> wrote:
>
> Le 01/09/2022 à 19:35, Suren Baghdasaryan a écrit :
> > Introduce find_and_lock_anon_vma function to lookup and lock an anonymous
> > VMA during page fault handling. When VMA is not found, can't be locked
> > or changes after being locked, the function returns NULL. The lookup is
> > performed under RCU protection to prevent the found VMA from being
> > destroyed before the VMA lock is acquired. VMA lock statistics are
> > updated according to the results.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> > include/linux/mm.h | 3 +++
> > mm/memory.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 48 insertions(+)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 7c3190eaabd7..a3cbaa7b9119 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -684,6 +684,9 @@ static inline void vma_assert_no_reader(struct vm_area_struct *vma)
> > vma);
> > }
> >
> > +struct vm_area_struct *find_and_lock_anon_vma(struct mm_struct *mm,
> > + unsigned long address);
> > +
> > #else /* CONFIG_PER_VMA_LOCK */
> >
> > static inline void vma_init_lock(struct vm_area_struct *vma) {}
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 29d2f49f922a..bf557f7056de 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5183,6 +5183,51 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
> > }
> > EXPORT_SYMBOL_GPL(handle_mm_fault);
> >
> > +#ifdef CONFIG_PER_VMA_LOCK
> > +static inline struct vm_area_struct *find_vma_under_rcu(struct mm_struct *mm,
> > + unsigned long address)
> > +{
> > + struct vm_area_struct *vma = __find_vma(mm, address);
> > +
> > + if (!vma || vma->vm_start > address)
> > + return NULL;
> > +
> > + if (!vma_is_anonymous(vma))
> > + return NULL;
> > +
>
> It looks to me more natural to first check that the VMA is part of the RB
> tree before try read locking it.
I think we want to check that the VMA is still part of the mm _after_
we locked it. Otherwise we might pass the check, then some other
thread does (lock->isolate->unlock) and then we lock the VMA. We would
end up with a VMA that is not part of mm anymore but we assume it is.
>
> > + if (!vma_read_trylock(vma)) {
> > + count_vm_vma_lock_event(VMA_LOCK_ABORT);
> > + return NULL;
> > + }
> > +
> > + /* Check if the VMA got isolated after we found it */
> > + if (RB_EMPTY_NODE(&vma->vm_rb)) {
> > + vma_read_unlock(vma);
> > + count_vm_vma_lock_event(VMA_LOCK_MISS);
> > + return NULL;
> > + }
> > +
> > + return vma;
> > +}
> > +
> > +/*
> > + * Lookup and lock and anonymous VMA. Returned VMA is guaranteed to be stable
> > + * and not isolated. If the VMA is not found of is being modified the function
> > + * returns NULL.
> > + */
> > +struct vm_area_struct *find_and_lock_anon_vma(struct mm_struct *mm,
> > + unsigned long address)
> > +{
> > + struct vm_area_struct *vma;
> > +
> > + rcu_read_lock();
> > + vma = find_vma_under_rcu(mm, address);
> > + rcu_read_unlock();
> > +
> > + return vma;
> > +}
> > +#endif /* CONFIG_PER_VMA_LOCK */
> > +
> > #ifndef __PAGETABLE_P4D_FOLDED
> > /*
> > * Allocate p4d page table.
>
Powered by blists - more mailing lists