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Message-ID: <CAAeHK+x-dihJ5+Zb1JBNaL5VK1zB87BR5kPX2B=q+FyVW+WHnw@mail.gmail.com>
Date: Wed, 23 Oct 2019 17:00:06 +0200
From: Andrey Konovalov <andreyknvl@...gle.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: USB list <linux-usb@...r.kernel.org>,
KVM list <kvm@...r.kernel.org>,
virtualization@...ts.linux-foundation.org,
netdev <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Alan Stern <stern@...land.harvard.edu>,
"Michael S . Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Arnd Bergmann <arnd@...db.de>,
Steven Rostedt <rostedt@...dmis.org>,
David Windsor <dwindsor@...il.com>,
Elena Reshetova <elena.reshetova@...el.com>,
Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH 3/3] vhost, kcov: collect coverage from vhost_worker
On Wed, Oct 23, 2019 at 3:50 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Wed, Oct 23, 2019 at 3:35 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
> >
> > On Wed, Oct 23, 2019 at 10:36 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > >
> > > On Tue, Oct 22, 2019 at 6:46 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
> > > >
> > > > This patch adds kcov_remote_start()/kcov_remote_stop() annotations to the
> > > > vhost_worker() function, which is responsible for processing vhost works.
> > > > Since vhost_worker() threads are spawned per vhost device instance
> > > > the common kcov handle is used for kcov_remote_start()/stop() annotations
> > > > (see Documentation/dev-tools/kcov.rst for details). As the result kcov can
> > > > now be used to collect coverage from vhost worker threads.
> > > >
> > > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > > > ---
> > > > drivers/vhost/vhost.c | 6 ++++++
> > > > drivers/vhost/vhost.h | 1 +
> > > > 2 files changed, 7 insertions(+)
> > > >
> > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > > index 36ca2cf419bf..a5a557c4b67f 100644
> > > > --- a/drivers/vhost/vhost.c
> > > > +++ b/drivers/vhost/vhost.c
> > > > @@ -30,6 +30,7 @@
> > > > #include <linux/sched/signal.h>
> > > > #include <linux/interval_tree_generic.h>
> > > > #include <linux/nospec.h>
> > > > +#include <linux/kcov.h>
> > > >
> > > > #include "vhost.h"
> > > >
> > > > @@ -357,7 +358,9 @@ static int vhost_worker(void *data)
> > > > llist_for_each_entry_safe(work, work_next, node, node) {
> > > > clear_bit(VHOST_WORK_QUEUED, &work->flags);
> > > > __set_current_state(TASK_RUNNING);
> > > > + kcov_remote_start(dev->kcov_handle);
> > > > work->fn(work);
> > > > + kcov_remote_stop();
> > > > if (need_resched())
> > > > schedule();
> > > > }
> > > > @@ -546,6 +549,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
> > > >
> > > > /* No owner, become one */
> > > > dev->mm = get_task_mm(current);
> > > > + dev->kcov_handle = current->kcov_handle;
> > >
> > > kcov_handle is not present in task_struct if !CONFIG_KCOV
> > >
> > > Also this does not use KCOV_SUBSYSTEM_COMMON.
> > > We discussed something along the following lines:
> > >
> > > u64 kcov_remote_handle(u64 subsys, u64 id)
> > > {
> > > WARN_ON(subsys or id has wrong bits set).
> >
> > Hm, we can't have warnings in kcov_remote_handle() that is exposed in
> > uapi headers. What we can do is return 0 (invalid handle) if subsys/id
> > have incorrect bits set. And then we can either have another
> > kcov_remote_handle() internally (with a different name though) that
> > has a warning, or have warning in kcov_remote_start(). WDYT?
>
> I would probably add the warning to kcov_remote_start(). This avoids
> the need for another function and will catch a wrong ID if caller
> generated it by some other means.
> And then ioctls should also detect bad handles passed in and return
> EINVAL. Then we will cover errors for both kernel and user programs.
OK, will do in v2.
>
> >
> > > return ...;
> > > }
> > >
> > > kcov_remote_handle(KCOV_SUBSYSTEM_USB, bus);
> > > kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, current->kcov_handle);
I'll add internal kcov_remote_handle_common() and
kcov_remote_handle_usb() helpers to simplify kcov hooks in usb/vhost
code though.
> > >
> > >
> > > > worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
> > > > if (IS_ERR(worker)) {
> > > > err = PTR_ERR(worker);
> > > > @@ -571,6 +575,7 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
> > > > if (dev->mm)
> > > > mmput(dev->mm);
> > > > dev->mm = NULL;
> > > > + dev->kcov_handle = 0;
> > > > err_mm:
> > > > return err;
> > > > }
> > > > @@ -682,6 +687,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > > > if (dev->worker) {
> > > > kthread_stop(dev->worker);
> > > > dev->worker = NULL;
> > > > + dev->kcov_handle = 0;
> > > > }
> > > > if (dev->mm)
> > > > mmput(dev->mm);
> > > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > > > index e9ed2722b633..a123fd70847e 100644
> > > > --- a/drivers/vhost/vhost.h
> > > > +++ b/drivers/vhost/vhost.h
> > > > @@ -173,6 +173,7 @@ struct vhost_dev {
> > > > int iov_limit;
> > > > int weight;
> > > > int byte_weight;
> > > > + u64 kcov_handle;
> > > > };
> > > >
> > > > bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);
> > > > --
> > > > 2.23.0.866.gb869b98d4c-goog
> > > >
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