From: Greg KH <gregkh@linuxfoundation.org>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Kees Cook <keescook@chromium.org>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will.deacon@arm.com>,
"Reshetova, Elena" <elena.reshetova@intel.com>,
Arnd Bergmann <arnd@arndb.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
David Windsor <dave@progbits.org>,
LKML <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: [RFC][PATCH 2/7] kref: Add kref_read()
Date: Wed, 16 Nov 2016 11:19:15 +0100 [thread overview]
Message-ID: <20161116101915.GB23902@kroah.com> (raw)
In-Reply-To: <582C30DF.60205@iogearbox.net>
On Wed, Nov 16, 2016 at 11:11:43AM +0100, Daniel Borkmann wrote:
> On 11/16/2016 09:21 AM, Greg KH wrote:
> > On Tue, Nov 15, 2016 at 12:53:35PM -0800, Kees Cook wrote:
> > > On Tue, Nov 15, 2016 at 12:03 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > > > On Tue, Nov 15, 2016 at 08:33:22AM +0100, Greg KH wrote:
> > > > > On Mon, Nov 14, 2016 at 06:39:48PM +0100, Peter Zijlstra wrote:
> > > >
> > > > > > --- a/drivers/block/drbd/drbd_req.c
> > > > > > +++ b/drivers/block/drbd/drbd_req.c
> > > > > > @@ -520,7 +520,7 @@ static void mod_rq_state(struct drbd_req
> > > > > > /* Completion does it's own kref_put. If we are going to
> > > > > > * kref_sub below, we need req to be still around then. */
> > > > > > int at_least = k_put + !!c_put;
> > > > > > - int refcount = atomic_read(&req->kref.refcount);
> > > > > > + int refcount = kref_read(&req->kref);
> > > > > > if (refcount < at_least)
> > > > > > drbd_err(device,
> > > > > > "mod_rq_state: Logic BUG: %x -> %x: refcount = %d, should be >= %d\n",
> > > > >
> > > > > As proof of "things you should never do", here is one such example.
> > > > >
> > > > > ugh.
> > > > >
> > > > > > --- a/drivers/block/virtio_blk.c
> > > > > > +++ b/drivers/block/virtio_blk.c
> > > > > > @@ -767,7 +767,7 @@ static void virtblk_remove(struct virtio
> > > > > > /* Stop all the virtqueues. */
> > > > > > vdev->config->reset(vdev);
> > > > > >
> > > > > > - refc = atomic_read(&disk_to_dev(vblk->disk)->kobj.kref.refcount);
> > > > > > + refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref);
> > > > > > put_disk(vblk->disk);
> > > > > > vdev->config->del_vqs(vdev);
> > > > > > kfree(vblk->vqs);
> > > > >
> > > > > And this too, ugh, that's a huge abuse and is probably totally wrong...
> > > > >
> > > > > thanks again for digging through this crap. I wonder if we need to name
> > > > > the kref reference variable "do_not_touch_this_ever" or some such thing
> > > > > to catch all of the people who try to be "too smart".
> > > >
> > > > There's unimaginable bong hits involved in this stuff, in the end I
> > > > resorted to brute force and scripts to convert all this.
> > >
> > > What should we do about things like this (bpf_prog_put() and callbacks
> > > from kernel/bpf/syscall.c):
>
> Just reading up on this series. Your question refers to converting bpf
> prog and map ref counts to Peter's refcount_t eventually, right?
>
> > > static void bpf_prog_uncharge_memlock(struct bpf_prog *prog)
> > > {
> > > struct user_struct *user = prog->aux->user;
> > >
> > > atomic_long_sub(prog->pages, &user->locked_vm);
> >
> > Oh that's scary. Let's just make one reference count rely on another
> > one and not check things...
>
> Sorry, could you elaborate what you mean by 'check things', you mean for
> wrap around? IIUC, back then accounting was roughly similar modeled after
> perf event's one, and in this case accounts for pages used by progs and
> maps during their life-time. Are you suggesting that this approach is
> inherently broken?
No, it is correct, I responded too quickly before my morning coffee had
kicked in, my apologies.
greg k-h
next prev parent reply other threads:[~2016-11-16 10:19 UTC|newest]
Thread overview: 110+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-14 17:39 [RFC][PATCH 0/7] kref improvements Peter Zijlstra
2016-11-14 17:39 ` [RFC][PATCH 1/7] kref: Add KREF_INIT() Peter Zijlstra
2016-11-14 17:39 ` [RFC][PATCH 2/7] kref: Add kref_read() Peter Zijlstra
2016-11-14 18:16 ` Christoph Hellwig
2016-11-15 7:28 ` Greg KH
2016-11-15 7:47 ` Peter Zijlstra
2016-11-15 8:37 ` [PATCH] printk, locking/atomics, kref: Introduce new %pAr and %pAk format string options for atomic_t and 'struct kref' Ingo Molnar
2016-11-15 8:43 ` [PATCH v2] " Ingo Molnar
2016-11-15 9:21 ` Peter Zijlstra
2016-11-15 9:41 ` [PATCH v3] printk, locking/atomics, kref: Introduce new %pAa " Ingo Molnar
2016-11-15 10:10 ` [PATCH v2] printk, locking/atomics, kref: Introduce new %pAr " kbuild test robot
2016-11-15 16:42 ` [PATCH] " Linus Torvalds
2016-11-16 8:13 ` Ingo Molnar
2016-11-15 7:33 ` [RFC][PATCH 2/7] kref: Add kref_read() Greg KH
2016-11-15 8:03 ` Peter Zijlstra
2016-11-15 20:53 ` Kees Cook
2016-11-16 8:21 ` Greg KH
2016-11-16 10:10 ` Peter Zijlstra
2016-11-16 10:18 ` Greg KH
2016-11-16 10:11 ` Daniel Borkmann
2016-11-16 10:19 ` Greg KH [this message]
2016-11-16 10:09 ` Peter Zijlstra
2016-11-16 18:58 ` Kees Cook
2016-11-17 8:34 ` Peter Zijlstra
2016-11-17 12:30 ` David Windsor
2016-11-17 12:43 ` Peter Zijlstra
2016-11-17 13:01 ` Reshetova, Elena
2016-11-17 13:22 ` Peter Zijlstra
2016-11-17 15:42 ` Reshetova, Elena
2016-11-17 18:02 ` Reshetova, Elena
2016-11-17 19:10 ` Peter Zijlstra
2016-11-17 19:29 ` Peter Zijlstra
2016-11-17 19:34 ` Kees Cook
2016-11-14 17:39 ` [RFC][PATCH 3/7] kref: Kill kref_sub() Peter Zijlstra
2016-11-14 17:39 ` [RFC][PATCH 4/7] kref: Use kref_get_unless_zero() more Peter Zijlstra
2016-11-14 17:39 ` [RFC][PATCH 5/7] kref: Implement kref_put_lock() Peter Zijlstra
2016-11-14 20:35 ` Kees Cook
2016-11-15 7:50 ` Peter Zijlstra
2016-11-14 17:39 ` [RFC][PATCH 6/7] kref: Avoid more abuse Peter Zijlstra
2016-11-14 17:39 ` [RFC][PATCH 7/7] kref: Implement using refcount_t Peter Zijlstra
2016-11-15 8:40 ` Ingo Molnar
2016-11-15 9:47 ` Peter Zijlstra
2016-11-15 10:03 ` Ingo Molnar
2016-11-15 10:46 ` Peter Zijlstra
2016-11-15 13:03 ` Ingo Molnar
2016-11-15 18:06 ` Kees Cook
2016-11-15 19:16 ` Peter Zijlstra
2016-11-15 19:23 ` Kees Cook
2016-11-16 8:31 ` Ingo Molnar
2016-11-16 8:51 ` Greg KH
2016-11-16 9:07 ` Ingo Molnar
2016-11-16 9:24 ` Greg KH
2016-11-16 10:15 ` Peter Zijlstra
2016-11-16 18:55 ` Kees Cook
2016-11-17 8:33 ` Peter Zijlstra
2016-11-17 19:50 ` Kees Cook
2016-11-16 18:41 ` Kees Cook
2016-11-15 12:33 ` Boqun Feng
2016-11-15 13:01 ` Peter Zijlstra
2016-11-15 14:19 ` Boqun Feng
2016-11-17 9:28 ` Peter Zijlstra
2016-11-17 9:48 ` Boqun Feng
2016-11-17 10:29 ` Peter Zijlstra
2016-11-17 10:39 ` Peter Zijlstra
2016-11-17 11:03 ` Greg KH
2016-11-17 12:48 ` Peter Zijlstra
[not found] ` <CAL0jBu-GnREUPSX4kUDp-Cc8ZGp6+Cb2q0HVandswcLzPRnChQ@mail.gmail.com>
2016-11-17 12:08 ` Peter Zijlstra
2016-11-17 12:08 ` Will Deacon
2016-11-17 16:11 ` Peter Zijlstra
2016-11-17 16:36 ` Will Deacon
2016-11-18 8:26 ` Boqun Feng
2016-11-18 10:16 ` Will Deacon
2016-11-18 10:07 ` Reshetova, Elena
2016-11-18 11:37 ` Peter Zijlstra
2016-11-18 17:06 ` Will Deacon
2016-11-18 18:57 ` Peter Zijlstra
2016-11-21 4:06 ` Boqun Feng
2016-11-21 7:48 ` Ingo Molnar
2016-11-21 8:38 ` Boqun Feng
2016-11-21 8:44 ` Boqun Feng
2016-11-21 9:02 ` Peter Zijlstra
2016-11-21 9:37 ` Boqun Feng
2016-11-18 10:47 ` Reshetova, Elena
2016-11-18 10:52 ` Peter Zijlstra
2016-11-18 16:58 ` Reshetova, Elena
2016-11-18 18:53 ` Peter Zijlstra
2016-11-19 7:14 ` Reshetova, Elena
2016-11-19 11:45 ` Peter Zijlstra
2017-01-26 23:14 ` Kees Cook
2017-01-27 9:58 ` Peter Zijlstra
2017-01-27 21:07 ` Kees Cook
2017-01-30 13:40 ` Peter Zijlstra
2016-11-15 7:27 ` [RFC][PATCH 0/7] kref improvements Greg KH
2016-11-15 7:42 ` Ingo Molnar
2016-11-15 15:05 ` Greg KH
2016-11-15 7:48 ` Peter Zijlstra
2016-11-16 20:08 [RFC][PATCH 2/7] kref: Add kref_read() Alexei Starovoitov
2016-11-17 8:53 ` Peter Zijlstra
2016-11-17 16:19 ` Alexei Starovoitov
2016-11-17 16:34 ` Thomas Gleixner
2016-11-18 17:33 ` Reshetova, Elena
2016-11-19 3:47 ` Alexei Starovoitov
2016-11-21 8:18 ` Reshetova, Elena
2016-11-21 12:47 ` David Windsor
2016-11-21 15:39 ` Reshetova, Elena
2016-11-21 15:49 ` Peter Zijlstra
2016-11-21 16:00 ` Peter Zijlstra
2016-11-21 19:27 ` Reshetova, Elena
2016-11-21 20:12 ` David Windsor
2016-11-22 10:37 ` Peter Zijlstra
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