* [PATCH] kprobes: Document how optimized kprobes are removed from module unload
@ 2017-05-16 18:58 Steven Rostedt
2017-05-17 1:47 ` Masami Hiramatsu
0 siblings, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2017-05-16 18:58 UTC (permalink / raw)
To: Masami Hiramatsu; +Cc: LKML, Thomas Gleixner, Ingo Molnar
From: Steven Rostedt (VMware) <rostedt@goodmis.org>
Thomas discovered a bug where the kprobe trace tests had a race
condition where the kprobe_optimizer called from a delayed work queue
that does the optimizing and "unoptimizing" of a kprobe, can try to
modify the text after it has been freed by the init code.
The kprobe trace selftest is a special case, and Thomas and myself
investigated to see if there's a chance that this could also be a bug
with module unloading, as the code is not obvious to how it handles
this. After adding lots of printks, I figured it out. Thomas suggested
that this should be commented so that others will not have to go
through this exercise again.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 7367e0e..ac386f6 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2183,6 +2183,12 @@ static int kprobes_module_callback(struct notifier_block *nb,
* The vaddr this probe is installed will soon
* be vfreed buy not synced to disk. Hence,
* disarming the breakpoint isn't needed.
+ *
+ * Note, this will also move any optimized probes
+ * that are pending to be removed from their
+ * corresponding lists to the freeing_list and
+ * will not be touched by the delayed
+ * kprobe_optimizer work handler.
*/
kill_kprobe(p);
}
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] kprobes: Document how optimized kprobes are removed from module unload
2017-05-16 18:58 [PATCH] kprobes: Document how optimized kprobes are removed from module unload Steven Rostedt
@ 2017-05-17 1:47 ` Masami Hiramatsu
2017-05-17 2:46 ` Steven Rostedt
0 siblings, 1 reply; 4+ messages in thread
From: Masami Hiramatsu @ 2017-05-17 1:47 UTC (permalink / raw)
To: Steven Rostedt; +Cc: LKML, Thomas Gleixner, Ingo Molnar
On Tue, 16 May 2017 14:58:35 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> From: Steven Rostedt (VMware) <rostedt@goodmis.org>
>
> Thomas discovered a bug where the kprobe trace tests had a race
> condition where the kprobe_optimizer called from a delayed work queue
> that does the optimizing and "unoptimizing" of a kprobe, can try to
> modify the text after it has been freed by the init code.
>
> The kprobe trace selftest is a special case, and Thomas and myself
> investigated to see if there's a chance that this could also be a bug
> with module unloading, as the code is not obvious to how it handles
> this. After adding lots of printks, I figured it out. Thomas suggested
> that this should be commented so that others will not have to go
> through this exercise again.
>
OK, and I prefer this comment to move into kill_kprobe() right
before calling kill_optimized_kprobe() because that actually
does it.
Thank you,
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 7367e0e..ac386f6 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2183,6 +2183,12 @@ static int kprobes_module_callback(struct notifier_block *nb,
> * The vaddr this probe is installed will soon
> * be vfreed buy not synced to disk. Hence,
> * disarming the breakpoint isn't needed.
> + *
> + * Note, this will also move any optimized probes
> + * that are pending to be removed from their
> + * corresponding lists to the freeing_list and
> + * will not be touched by the delayed
> + * kprobe_optimizer work handler.
> */
> kill_kprobe(p);
> }
--
Masami Hiramatsu <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kprobes: Document how optimized kprobes are removed from module unload
2017-05-17 1:47 ` Masami Hiramatsu
@ 2017-05-17 2:46 ` Steven Rostedt
2017-05-17 4:00 ` Masami Hiramatsu
0 siblings, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2017-05-17 2:46 UTC (permalink / raw)
To: Masami Hiramatsu; +Cc: LKML, Thomas Gleixner, Ingo Molnar
On Wed, 17 May 2017 10:47:07 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:
> On Tue, 16 May 2017 14:58:35 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > From: Steven Rostedt (VMware) <rostedt@goodmis.org>
> >
> > Thomas discovered a bug where the kprobe trace tests had a race
> > condition where the kprobe_optimizer called from a delayed work queue
> > that does the optimizing and "unoptimizing" of a kprobe, can try to
> > modify the text after it has been freed by the init code.
> >
> > The kprobe trace selftest is a special case, and Thomas and myself
> > investigated to see if there's a chance that this could also be a bug
> > with module unloading, as the code is not obvious to how it handles
> > this. After adding lots of printks, I figured it out. Thomas suggested
> > that this should be commented so that others will not have to go
> > through this exercise again.
> >
>
> OK, and I prefer this comment to move into kill_kprobe() right
> before calling kill_optimized_kprobe() because that actually
> does it.
Actually, I can add a comment in both places. I didn't put it into
kill_kprobe() because, yes that's where it is done. I placed it in the
module handler because that's where one will look to see if module
unloading doesn't have any race conditions with the delayed handling.
-- Steve
>
> Thank you,
>
> > Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > ---
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index 7367e0e..ac386f6 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -2183,6 +2183,12 @@ static int kprobes_module_callback(struct notifier_block *nb,
> > * The vaddr this probe is installed will soon
> > * be vfreed buy not synced to disk. Hence,
> > * disarming the breakpoint isn't needed.
> > + *
> > + * Note, this will also move any optimized probes
> > + * that are pending to be removed from their
> > + * corresponding lists to the freeing_list and
> > + * will not be touched by the delayed
> > + * kprobe_optimizer work handler.
> > */
> > kill_kprobe(p);
> > }
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] kprobes: Document how optimized kprobes are removed from module unload
2017-05-17 2:46 ` Steven Rostedt
@ 2017-05-17 4:00 ` Masami Hiramatsu
0 siblings, 0 replies; 4+ messages in thread
From: Masami Hiramatsu @ 2017-05-17 4:00 UTC (permalink / raw)
To: Steven Rostedt; +Cc: LKML, Thomas Gleixner, Ingo Molnar
On Tue, 16 May 2017 22:46:02 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Wed, 17 May 2017 10:47:07 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > On Tue, 16 May 2017 14:58:35 -0400
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > From: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > >
> > > Thomas discovered a bug where the kprobe trace tests had a race
> > > condition where the kprobe_optimizer called from a delayed work queue
> > > that does the optimizing and "unoptimizing" of a kprobe, can try to
> > > modify the text after it has been freed by the init code.
> > >
> > > The kprobe trace selftest is a special case, and Thomas and myself
> > > investigated to see if there's a chance that this could also be a bug
> > > with module unloading, as the code is not obvious to how it handles
> > > this. After adding lots of printks, I figured it out. Thomas suggested
> > > that this should be commented so that others will not have to go
> > > through this exercise again.
> > >
> >
> > OK, and I prefer this comment to move into kill_kprobe() right
> > before calling kill_optimized_kprobe() because that actually
> > does it.
>
> Actually, I can add a comment in both places. I didn't put it into
> kill_kprobe() because, yes that's where it is done. I placed it in the
> module handler because that's where one will look to see if module
> unloading doesn't have any race conditions with the delayed handling.
OK, I see.
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Thanks,
>
> -- Steve
>
>
> >
> > Thank you,
> >
> > > Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> > > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > > ---
> > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > > index 7367e0e..ac386f6 100644
> > > --- a/kernel/kprobes.c
> > > +++ b/kernel/kprobes.c
> > > @@ -2183,6 +2183,12 @@ static int kprobes_module_callback(struct notifier_block *nb,
> > > * The vaddr this probe is installed will soon
> > > * be vfreed buy not synced to disk. Hence,
> > > * disarming the breakpoint isn't needed.
> > > + *
> > > + * Note, this will also move any optimized probes
> > > + * that are pending to be removed from their
> > > + * corresponding lists to the freeing_list and
> > > + * will not be touched by the delayed
> > > + * kprobe_optimizer work handler.
> > > */
> > > kill_kprobe(p);
> > > }
> >
> >
>
--
Masami Hiramatsu <mhiramat@kernel.org>
^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-05-16 18:58 [PATCH] kprobes: Document how optimized kprobes are removed from module unload Steven Rostedt
2017-05-17 1:47 ` Masami Hiramatsu
2017-05-17 2:46 ` Steven Rostedt
2017-05-17 4:00 ` Masami Hiramatsu
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