From: Andrei Vagin <avagin-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>
To: Cyrill Gorcunov <gorcunov-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Jann Horn <jannh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kernel list
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
akpm-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org,
xemul-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org,
Michael Kerrisk-manpages
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
avagin-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org,
jbaron-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org,
Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Subject: Re: [patch v4 resend 2/2] kcmp: Add KCMP_EPOLL_TFD mode to compare epoll target files
Date: Fri, 12 May 2017 18:45:09 -0700 [thread overview]
Message-ID: <20170513014508.GA21900@outlook.office365.com> (raw)
In-Reply-To: <20170512225340.GD1881-ZmlpmtaulQd+urZeOPWqwQ@public.gmane.org>
On Sat, May 13, 2017 at 01:53:40AM +0300, Cyrill Gorcunov wrote:
> On Sat, May 13, 2017 at 12:41:30AM +0200, Jann Horn wrote:
> > [resending as plaintext]
> >
> > I realize that the existing kcmp code has the same issue, but:
> >
> > Why are you not taking a reference to filp or filp_tgt? This can end up
> > performing a comparison between a pointer to a freed struct file and a
> > pointer to a struct file that was allocated afterwards, right? So it can
> > return a false "is equal" result when the two files aren't actually the same
> > if one of the target tasks is running? This looks like it unnecessarily
> > exposes information about whether an allocation reuses the memory of
> > a previously freed allocation.
>
> It work with unlocked data on purpose for speed sake. Moreover even
> if we grap a reference it is valid _only_ during comparision operation,
> next we drop ref and it can be easily freed by os. Thus it's up to
> a caller to keep references to files/task and other resources used.
Looks like we can take rcu_read_lock() to guarantee that these objects
will not be freed, and rcu_read_lock() should not affect perfomance too much.
>
> Cyrill
next prev parent reply other threads:[~2017-05-13 1:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-24 15:39 [patch v4 resend 2/2] kcmp: Add KCMP_EPOLL_TFD mode to compare epoll target files Cyrill Gorcunov
[not found] ` <20170424154423.511592110-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2017-05-12 22:00 ` Andrew Morton
[not found] ` <20170512150018.b931c7f5295dd7484845fcec-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
2017-05-12 22:14 ` Cyrill Gorcunov
2017-05-12 22:41 ` Jann Horn
2017-05-12 22:53 ` Cyrill Gorcunov
[not found] ` <20170512225340.GD1881-ZmlpmtaulQd+urZeOPWqwQ@public.gmane.org>
2017-05-13 1:45 ` Andrei Vagin [this message]
[not found] ` <20170513014508.GA21900-1ViLX0X+lBJGNQ1M2rI3KwRV3xvJKrda@public.gmane.org>
2017-05-13 6:55 ` Cyrill Gorcunov
[not found] ` <20170513065514.GE1881-ZmlpmtaulQd+urZeOPWqwQ@public.gmane.org>
2017-05-13 7:15 ` Cyrill Gorcunov
2017-09-17 16:01 ` [v4,resend,2/2] " Eugene Syromiatnikov
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