From: Jiri Slaby <jslaby@suse.cz>
To: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, jirislaby@gmail.com,
Vojtech Pavlik <vojtech@suse.cz>, Michael Matz <matz@suse.de>,
Jiri Kosina <jkosina@suse.cz>,
Steven Rostedt <rostedt@goodmis.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [RFC 03/16] kgr: initial code
Date: Wed, 14 May 2014 12:12:06 +0200 [thread overview]
Message-ID: <53734176.5000003@suse.cz> (raw)
In-Reply-To: <53733746.1040200@linux.vnet.ibm.com>
On 05/14/2014 11:28 AM, Aravinda Prasad wrote:
> On Wednesday 30 April 2014 08:00 PM, Jiri Slaby wrote:
>> From: Jiri Kosina <jkosina@suse.cz>
>>
>> Provide initial implementation. We are now able to do ftrace-based
>> runtime patching of the kernel code.
>>
>> In addition to that, we will provide a kgr_patcher module in the next
>> patch to test the functionality.
>
> Hi Jiri,
>
> Interesting! I have couple of comments:
>
> I think with kgraft (also with kpatch, though have not looked into
> it yet), the patched function cannot be dynamically ftraced.
> Though dynamic ftrace can be enabled on the new code, the user is
> required to know the function label of the new code. This could
> potentially break existing scripts. I think this should be documented.
Hi,
of course that the functions can be traced. Look, I turned on tracing
for capable, then patched, then turned on tracing for new_capable (which
is the patched function). So now, trace shows:
console-kit-dae-535 [001] ...1 181.729698: capable <-vt_ioctl
console-kit-dae-539 [001] ...1 181.729741: capable <-vt_ioctl
console-kit-dae-541 [000] .N.1 181.906014: capable <-vt_ioctl
systemd-1 [001] ...1 181.937328: capable <-SyS_epoll_ctl
sshd-662 [001] ...1 246.437561: capable <-sock_setsockopt
sshd-662 [001] ...1 246.437564: new_capable
<-sock_setsockopt
sshd-662 [001] ...1 246.444790: capable <-sock_setsockopt
sshd-662 [001] ...1 246.444793: new_capable
<-sock_setsockopt
dbus-daemon-128 [000] .N.1 246.456307: capable <-SyS_epoll_ctl
dbus-daemon-128 [000] ...1 246.456611: new_capable <-SyS_epoll_ctl
There is no limitation thanks to the use of the ftrace subsystem. We are
just another user, i.e. another piece of code called in a loop for a
particular fentry location.
>> +/*
>> + * The stub needs to modify the RIP value stored in struct pt_regs
>> + * so that ftrace redirects the execution properly.
>> + */
>> +#define KGR_STUB_ARCH_SLOW(_name, _new_function) \
>> +static void _new_function ##_stub_slow (unsigned long ip, unsigned long parent_ip, \
>> + struct ftrace_ops *ops, struct pt_regs *regs) \
>> +{ \
>> + struct kgr_loc_caches *c = ops->private; \
>> + \
>> + if (task_thread_info(current)->kgr_in_progress && current->mm) {\
>
> Is there a race here? The per task kgr_in_progress is set after
> the slow stub is registered in register_ftrace_function(). If the
> patched function is called in between it will be redirected to new code.
Hmm, that looks strange. I will look into that and the other comments
later (and comment separately). Thanks.
--
js
suse labs
next prev parent reply other threads:[~2014-05-14 10:12 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-30 14:30 [RFC 00/16] kGraft Jiri Slaby
2014-04-30 14:30 ` [RFC 01/16] ftrace: Add function to find fentry of function Jiri Slaby
2014-04-30 14:48 ` Steven Rostedt
2014-04-30 14:58 ` Jiri Slaby
2014-04-30 14:30 ` [RFC 02/16] ftrace: Make ftrace_is_dead available globally Jiri Slaby
2014-04-30 14:30 ` [RFC 03/16] kgr: initial code Jiri Slaby
2014-04-30 14:56 ` Steven Rostedt
2014-04-30 14:57 ` Jiri Slaby
2014-05-01 20:20 ` Andi Kleen
2014-05-01 20:37 ` Jiri Kosina
2014-05-14 9:28 ` Aravinda Prasad
2014-05-14 10:12 ` Jiri Slaby [this message]
2014-05-14 10:41 ` Aravinda Prasad
2014-05-14 10:44 ` Jiri Slaby
2014-05-14 11:19 ` Aravinda Prasad
2014-05-20 11:36 ` Jiri Slaby
2014-05-21 18:28 ` Aravinda Prasad
2014-05-26 8:50 ` Jiri Kosina
2014-04-30 14:30 ` [RFC 04/16] kgr: add testing kgraft patch Jiri Slaby
2014-05-06 11:03 ` Pavel Machek
2014-05-12 12:50 ` Jiri Slaby
2014-04-30 14:30 ` [RFC 05/16] kgr: update Kconfig documentation Jiri Slaby
2014-05-03 14:32 ` Randy Dunlap
2014-04-30 14:30 ` [RFC 06/16] kgr: add Documentation Jiri Slaby
2014-05-06 11:03 ` Pavel Machek
2014-05-09 9:31 ` kgr: dealing with optimalizations? (was Re: [RFC 06/16] kgr: add Documentat)ion Pavel Machek
2014-05-09 12:22 ` Michael Matz
2014-04-30 14:30 ` [RFC 07/16] kgr: trigger the first check earlier Jiri Slaby
2014-04-30 14:30 ` [RFC 08/16] kgr: sched.h, introduce kgr_task_safe helper Jiri Slaby
2014-04-30 14:30 ` [RFC 09/16] kgr: mark task_safe in some kthreads Jiri Slaby
2014-04-30 15:49 ` Greg Kroah-Hartman
2014-04-30 16:55 ` Paul E. McKenney
2014-04-30 18:33 ` Vojtech Pavlik
2014-04-30 19:07 ` Paul E. McKenney
2014-05-01 14:24 ` Tejun Heo
2014-05-01 20:17 ` Jiri Kosina
2014-05-01 21:02 ` Tejun Heo
2014-05-01 21:09 ` Tejun Heo
2014-05-14 14:59 ` Jiri Slaby
2014-05-14 15:15 ` Vojtech Pavlik
2014-05-14 15:30 ` Paul E. McKenney
2014-05-14 16:32 ` Tejun Heo
2014-05-15 3:53 ` Mike Galbraith
2014-05-15 4:06 ` Tejun Heo
2014-05-15 4:46 ` Mike Galbraith
2014-05-15 4:50 ` Tejun Heo
2014-05-15 5:04 ` Mike Galbraith
2014-05-15 5:09 ` Tejun Heo
2014-05-15 5:32 ` Mike Galbraith
2014-05-15 6:05 ` Tejun Heo
2014-05-15 6:32 ` Mike Galbraith
2014-04-30 14:30 ` [RFC 10/16] kgr: kthreads support Jiri Slaby
2014-04-30 14:30 ` [RFC 11/16] kgr: handle irqs Jiri Slaby
2014-04-30 14:30 ` [RFC 12/16] kgr: add tools Jiri Slaby
2014-05-06 11:03 ` Pavel Machek
2014-04-30 14:30 ` [RFC 13/16] kgr: add MAINTAINERS entry Jiri Slaby
2014-04-30 14:30 ` [RFC 14/16] kgr: x86: refuse to build without fentry support Jiri Slaby
2014-04-30 14:30 ` [RFC 15/16] kgr: add procfs interface for per-process 'kgr_in_progress' Jiri Slaby
2014-04-30 14:30 ` [RFC 16/16] kgr: make a per-process 'in progress' flag a single bit Jiri Slaby
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