From: Miroslav Benes <mbenes@suse.cz>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Petr Mladek <pmladek@suse.com>, Jessica Yu <jeyu@redhat.com>,
Jiri Kosina <jikos@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
live-patching@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, Vojtech Pavlik <vojtech@suse.com>,
Jiri Slaby <jslaby@suse.cz>,
Chris J Arges <chris.j.arges@canonical.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v3 13/15] livepatch: change to a per-task consistency model
Date: Fri, 23 Dec 2016 10:24:35 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.20.1612231013470.5990@pobox.suse.cz> (raw)
In-Reply-To: <20161221212505.dbxeddu2skmjmwiq@treble>
> > > diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> > > index 5efa262..e79ebb5 100644
> > > --- a/kernel/livepatch/patch.c
> > > +++ b/kernel/livepatch/patch.c
> > > @@ -29,6 +29,7 @@
> > > #include <linux/bug.h>
> > > #include <linux/printk.h>
> > > #include "patch.h"
> > > +#include "transition.h"
> > >
> > > static LIST_HEAD(klp_ops);
> > >
> > > @@ -54,15 +55,53 @@ static void notrace klp_ftrace_handler(unsigned long ip,
> > > {
> > > struct klp_ops *ops;
> > > struct klp_func *func;
> > > + int patch_state;
> > >
> > > ops = container_of(fops, struct klp_ops, fops);
> > >
> > > rcu_read_lock();
> > > +
> > > func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
> > > stack_node);
> > > - if (WARN_ON_ONCE(!func))
> > > +
> > > + if (!func)
> > > goto unlock;
> >
> > Why do you removed the WARN_ON_ONCE(), please?
> >
> > We still add the function on the stack before registering
> > the ftrace handler. Also we unregister the ftrace handler
> > before removing the the last entry from the stack.
> >
> > AFAIK, unregister_ftrace_function() calls rcu_synchronize()'
> > to make sure that no-one is inside the handler once finished.
> > Mirek knows more about it.
>
> Hm, this is news to me. Mirek, please share :-)
Well, I think the whole thing is well described in emails I exchanged with
Steven few months ago. See [1].
[1] http://lkml.kernel.org/r/alpine.LNX.2.00.1608081041060.10833@pobox.suse.cz
> > If this is not true, we have a problem. For example,
> > we call kfree(ops) after unregister_ftrace_function();
>
> Agreed.
TL;DR - we should be ok as long as we do not do crazy things in the
handler, deliberate sleeping for example.
WARN_ON_ONCE() may be crazy too. I think we discussed it long ago and we
came to an agreement to remove it.
Miroslav, very slowly going through the patch set
next prev parent reply other threads:[~2016-12-23 9:24 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 18:08 [PATCH v3 00/15] livepatch: hybrid consistency model Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 01/15] stacktrace/x86: add function for detecting reliable stack traces Josh Poimboeuf
2016-12-16 13:07 ` Petr Mladek
2016-12-16 22:09 ` Josh Poimboeuf
2016-12-19 16:25 ` Miroslav Benes
2016-12-19 17:25 ` Josh Poimboeuf
2016-12-19 18:23 ` Miroslav Benes
2016-12-20 9:39 ` Petr Mladek
2016-12-20 21:21 ` Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 02/15] x86/entry: define _TIF_ALLWORK_MASK flags explicitly Josh Poimboeuf
2016-12-16 14:17 ` Petr Mladek
2016-12-16 22:13 ` Josh Poimboeuf
2016-12-19 16:39 ` Miroslav Benes
2017-01-10 8:49 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 03/15] livepatch: temporary stubs for klp_patch_pending() and klp_update_patch_state() Josh Poimboeuf
2016-12-16 14:41 ` Petr Mladek
2016-12-16 22:15 ` Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 04/15] livepatch/x86: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2016-12-08 18:27 ` Andy Lutomirski
2016-12-16 15:39 ` Petr Mladek
2016-12-21 13:54 ` Miroslav Benes
2017-01-11 7:06 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 05/15] livepatch/powerpc: " Josh Poimboeuf
2016-12-16 16:00 ` Petr Mladek
2016-12-21 14:30 ` Miroslav Benes
2017-01-10 8:29 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 06/15] livepatch/s390: reorganize TIF thread flag bits Josh Poimboeuf
2016-12-21 15:29 ` Miroslav Benes
2016-12-08 18:08 ` [PATCH v3 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 08/15] livepatch: separate enabled and patched states Josh Poimboeuf
2016-12-16 16:21 ` Petr Mladek
2016-12-23 12:54 ` Miroslav Benes
2017-01-10 9:10 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 09/15] livepatch: remove unnecessary object loaded check Josh Poimboeuf
2016-12-16 16:26 ` Petr Mladek
2016-12-23 12:58 ` Miroslav Benes
2017-01-10 9:14 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 10/15] livepatch: move patching functions into patch.c Josh Poimboeuf
2016-12-16 16:49 ` Petr Mladek
2016-12-23 13:06 ` Miroslav Benes
2017-01-10 9:15 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 11/15] livepatch: use kstrtobool() in enabled_store() Josh Poimboeuf
2016-12-16 16:55 ` Petr Mladek
2016-12-16 22:19 ` Josh Poimboeuf
2016-12-23 13:13 ` Miroslav Benes
2016-12-08 18:08 ` [PATCH v3 12/15] livepatch: store function sizes Josh Poimboeuf
2016-12-19 13:10 ` Petr Mladek
2016-12-23 13:40 ` Miroslav Benes
2017-01-11 10:09 ` Kamalesh Babulal
2016-12-08 18:08 ` [PATCH v3 13/15] livepatch: change to a per-task consistency model Josh Poimboeuf
2016-12-20 17:32 ` Petr Mladek
2016-12-21 21:25 ` Josh Poimboeuf
2016-12-22 14:34 ` Petr Mladek
2016-12-22 18:31 ` Josh Poimboeuf
2017-01-10 13:00 ` Petr Mladek
2017-01-10 20:46 ` Josh Poimboeuf
2017-01-11 15:18 ` Petr Mladek
2017-01-11 15:26 ` Josh Poimboeuf
2016-12-23 9:24 ` Miroslav Benes [this message]
2016-12-23 10:18 ` Petr Mladek
2017-01-06 20:07 ` Josh Poimboeuf
2017-01-10 10:40 ` Petr Mladek
2017-01-04 13:44 ` Miroslav Benes
2017-01-06 21:01 ` Josh Poimboeuf
2017-01-10 10:45 ` Miroslav Benes
2017-01-05 9:34 ` Miroslav Benes
2017-01-06 21:04 ` Josh Poimboeuf
2016-12-08 18:08 ` [PATCH v3 14/15] livepatch: add /proc/<pid>/patch_state Josh Poimboeuf
2016-12-21 11:20 ` Petr Mladek
2017-01-04 14:50 ` Miroslav Benes
2016-12-08 18:08 ` [PATCH v3 15/15] livepatch: allow removal of a disabled patch Josh Poimboeuf
2016-12-21 14:44 ` Petr Mladek
2017-01-04 14:57 ` Miroslav Benes
2017-01-06 21:04 ` Josh Poimboeuf
2016-12-10 5:46 ` [PATCH v3 00/15] livepatch: hybrid consistency model Balbir Singh
2016-12-10 17:17 ` Josh Poimboeuf
2016-12-11 2:08 ` Balbir Singh
2016-12-12 14:04 ` Josh Poimboeuf
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