[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAJuCfpH8-wNiPXQcS=0j-Ex7iMqoBkUhjSN8QiAvq6FdXudRGQ@mail.gmail.com>
Date: Tue, 17 Jan 2023 17:53:00 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Michal Hocko <mhocko@...e.com>
Cc: akpm@...ux-foundation.org, michel@...pinasse.org,
jglisse@...gle.com, vbabka@...e.cz, hannes@...xchg.org,
mgorman@...hsingularity.net, dave@...olabs.net,
willy@...radead.org, liam.howlett@...cle.com, peterz@...radead.org,
ldufour@...ux.ibm.com, 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,
punit.agrawal@...edance.com, lstoakes@...il.com,
peterjung1337@...il.com, rientjes@...gle.com,
axelrasmussen@...gle.com, joelaf@...gle.com, minchan@...gle.com,
jannh@...gle.com, shakeelb@...gle.com, tatashin@...gle.com,
edumazet@...gle.com, gthelen@...gle.com, gurua@...gle.com,
arjunroy@...gle.com, soheil@...gle.com, hughlynch@...gle.com,
leewalsh@...gle.com, posk@...gle.com, linux-mm@...ck.org,
linux-arm-kernel@...ts.infradead.org,
linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 26/41] kernel/fork: assert no VMA readers during its destruction
On Tue, Jan 17, 2023 at 7:42 AM 'Michal Hocko' via kernel-team
<kernel-team@...roid.com> wrote:
>
> On Mon 09-01-23 12:53:21, Suren Baghdasaryan wrote:
> > Assert there are no holders of VMA lock for reading when it is about to be
> > destroyed.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> > include/linux/mm.h | 8 ++++++++
> > kernel/fork.c | 2 ++
> > 2 files changed, 10 insertions(+)
> >
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 594e835bad9c..c464fc8a514c 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -680,6 +680,13 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma)
> > VM_BUG_ON_VMA(vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq), vma);
> > }
> >
> > +static inline void vma_assert_no_reader(struct vm_area_struct *vma)
> > +{
> > + VM_BUG_ON_VMA(rwsem_is_locked(&vma->lock) &&
> > + vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq),
> > + vma);
>
> Do we really need to check for vm_lock_seq? rwsem_is_locked should tell
> us something is wrong on its own, no? This could be somebody racing with
> the vma destruction and using the write lock. Unlikely but I do not see
> why to narrow debugging scope.
I wanted to ensure there are no page fault handlers (read-lockers)
when we are destroying the VMA and rwsem_is_locked(&vma->lock) alone
could trigger if someone is concurrently calling vma_write_lock(). But
I don't think we expect someone to be write-locking the VMA while we
are destroying it, so you are right, I'm overcomplicating things here.
I think I can get rid of vma_assert_no_reader() and add
VM_BUG_ON_VMA(rwsem_is_locked(&vma->lock)) directly in
__vm_area_free(). WDYT?
> --
> Michal Hocko
> SUSE Labs
>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@...roid.com.
>
Powered by blists - more mailing lists