From: Oleg Nesterov <oleg@redhat.com>
To: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Davidlohr Bueso <dave@stgolabs.net>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: fix lockdep build in rcu-protected get_mm_exe_file()
Date: Tue, 24 Mar 2015 20:02:29 +0100 [thread overview]
Message-ID: <20150324190229.GC11834@redhat.com> (raw)
In-Reply-To: <CALYGNiP15BLtxMmMnpEu94jZBtce7tCtJnavrguqFr1d2XxH_A@mail.gmail.com>
On 03/24, Konstantin Khlebnikov wrote:
>
> On Tue, Mar 24, 2015 at 9:10 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> >>>
> >>> "atomic_read(&mm->mm_users) <= 1" looks a bit more "safe". But again,
> >>> I won't insist.
> >>
> >> Not so safe: this will race with get_task_mm().
> >
> > How?
>
> I mean rcu/lockdep debug migh race with get_task_mm() and generate
> false-positive warning about non-protected rcu_dereference.
Still can't understand, I think it can't... and if it could, then this
warning would not be false positive.
Anut this doesn't matter because we seem to agree this check should go away.
> > Yeees, probably rcu_dereference_raw() would be even better. set_mm_exe_file()
> > must be called only if nobody but us can access this mm.
>
> Yep.
Great. Davidlohr will you agree?
Oleg.
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WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Davidlohr Bueso <dave@stgolabs.net>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: fix lockdep build in rcu-protected get_mm_exe_file()
Date: Tue, 24 Mar 2015 20:02:29 +0100 [thread overview]
Message-ID: <20150324190229.GC11834@redhat.com> (raw)
In-Reply-To: <CALYGNiP15BLtxMmMnpEu94jZBtce7tCtJnavrguqFr1d2XxH_A@mail.gmail.com>
On 03/24, Konstantin Khlebnikov wrote:
>
> On Tue, Mar 24, 2015 at 9:10 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> >>>
> >>> "atomic_read(&mm->mm_users) <= 1" looks a bit more "safe". But again,
> >>> I won't insist.
> >>
> >> Not so safe: this will race with get_task_mm().
> >
> > How?
>
> I mean rcu/lockdep debug migh race with get_task_mm() and generate
> false-positive warning about non-protected rcu_dereference.
Still can't understand, I think it can't... and if it could, then this
warning would not be false positive.
Anut this doesn't matter because we seem to agree this check should go away.
> > Yeees, probably rcu_dereference_raw() would be even better. set_mm_exe_file()
> > must be called only if nobody but us can access this mm.
>
> Yep.
Great. Davidlohr will you agree?
Oleg.
next prev parent reply other threads:[~2015-03-24 19:04 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-20 14:47 [PATCH] mm: fix lockdep build in rcu-protected get_mm_exe_file() Konstantin Khlebnikov
2015-03-20 14:47 ` Konstantin Khlebnikov
2015-03-23 18:11 ` Davidlohr Bueso
2015-03-23 18:11 ` Davidlohr Bueso
2015-03-23 19:10 ` Oleg Nesterov
2015-03-23 19:10 ` Oleg Nesterov
2015-03-24 14:38 ` Davidlohr Bueso
2015-03-24 14:38 ` Davidlohr Bueso
2015-03-24 17:13 ` Konstantin Khlebnikov
2015-03-24 17:13 ` Konstantin Khlebnikov
2015-03-24 18:10 ` Oleg Nesterov
2015-03-24 18:10 ` Oleg Nesterov
2015-03-24 18:15 ` Konstantin Khlebnikov
2015-03-24 18:15 ` Konstantin Khlebnikov
2015-03-24 19:02 ` Oleg Nesterov [this message]
2015-03-24 19:02 ` Oleg Nesterov
2015-03-25 1:30 ` [PATCH v2] prctl: avoid using mmap_sem for exe_file serialization Davidlohr Bueso
2015-03-25 1:30 ` Davidlohr Bueso
2015-03-25 9:21 ` Konstantin Khlebnikov
2015-03-25 9:21 ` Konstantin Khlebnikov
2015-03-25 10:42 ` [PATCH v3] " Davidlohr Bueso
2015-03-25 10:42 ` Davidlohr Bueso
2015-03-25 11:08 ` Konstantin Khlebnikov
2015-03-25 11:08 ` Konstantin Khlebnikov
2015-03-25 12:50 ` Davidlohr Bueso
2015-03-25 12:50 ` Davidlohr Bueso
2015-03-25 12:53 ` Oleg Nesterov
2015-03-25 12:53 ` Oleg Nesterov
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