2018-12-05 18:34:14

by Steven Rostedt

Subject: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

From: "Steven Rostedt (VMware)" <[email protected]>

It has been reported that ftrace_replace_code() which is called by
ftrace_modify_all_code() can cause a soft lockup warning for an
allmodconfig kernel. This is because all the debug options enabled
causes the loop in ftrace_replace_code() (which loops over all the
functions being enabled where there can be 10s of thousands), is too
slow, and never schedules out.

To solve this, setting FTRACE_SCHEDULABLE to the command passed into
ftrace_replace_code() will make it call cond_resched() in the loop,
which prevents the soft lockup warning from triggering.

Link: http://lkml.kernel.org/r/[email protected]

Reported-by: Anders Roxell <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
---
arch/arm64/kernel/ftrace.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index 57e962290df3..9a8de0a79f97 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,

void arch_ftrace_update_code(int command)
{
+ command |= FTRACE_SCHEDULABLE;
ftrace_modify_all_code(command);
}

--
2.19.1

2018-12-06 13:23:05

by Will Deacon

Subject: Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

On Wed, Dec 05, 2018 at 12:48:54PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <[email protected]>
>
> It has been reported that ftrace_replace_code() which is called by
> ftrace_modify_all_code() can cause a soft lockup warning for an
> allmodconfig kernel. This is because all the debug options enabled
> causes the loop in ftrace_replace_code() (which loops over all the
> functions being enabled where there can be 10s of thousands), is too
> slow, and never schedules out.
>
> To solve this, setting FTRACE_SCHEDULABLE to the command passed into
> ftrace_replace_code() will make it call cond_resched() in the loop,
> which prevents the soft lockup warning from triggering.
>
> Link: http://lkml.kernel.org/r/[email protected]
>
> Reported-by: Anders Roxell <[email protected]>
> Signed-off-by: Steven Rostedt (VMware) <[email protected]>
> ---
> arch/arm64/kernel/ftrace.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 57e962290df3..9a8de0a79f97 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>
> void arch_ftrace_update_code(int command)
> {
> + command |= FTRACE_SCHEDULABLE;
> ftrace_modify_all_code(command);
> }

Bikeshed: I'd probably go for FTRACE_MAY_SLEEP, but I'm not going to die
on that hill so...

Acked-by: Will Deacon <[email protected]>

Thanks, Steve!

Will

2018-12-06 14:35:23

by Anders Roxell

Subject: Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

On Thu, 6 Dec 2018 at 14:19, Will Deacon <[email protected]> wrote:
>
> On Wed, Dec 05, 2018 at 12:48:54PM -0500, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <[email protected]>
> >
> > It has been reported that ftrace_replace_code() which is called by
> > ftrace_modify_all_code() can cause a soft lockup warning for an
> > allmodconfig kernel. This is because all the debug options enabled
> > causes the loop in ftrace_replace_code() (which loops over all the
> > functions being enabled where there can be 10s of thousands), is too
> > slow, and never schedules out.
> >
> > To solve this, setting FTRACE_SCHEDULABLE to the command passed into
> > ftrace_replace_code() will make it call cond_resched() in the loop,
> > which prevents the soft lockup warning from triggering.
> >
> > Link: http://lkml.kernel.org/r/[email protected]
> >
> > Reported-by: Anders Roxell <[email protected]>
> > Signed-off-by: Steven Rostedt (VMware) <[email protected]>
> > ---
> > arch/arm64/kernel/ftrace.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> > index 57e962290df3..9a8de0a79f97 100644
> > --- a/arch/arm64/kernel/ftrace.c
> > +++ b/arch/arm64/kernel/ftrace.c
> > @@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
> >
> > void arch_ftrace_update_code(int command)
> > {
> > + command |= FTRACE_SCHEDULABLE;
> > ftrace_modify_all_code(command);
> > }
>
> Bikeshed: I'd probably go for FTRACE_MAY_SLEEP, but I'm not going to die
> on that hill so...
>
> Acked-by: Will Deacon <[email protected]>

Tested-by: Anders Roxell <[email protected]>

Cheers,
Anders

>
> Thanks, Steve!
>
> Will

2018-12-06 16:00:17

by Steven Rostedt

Subject: Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

On Thu, 6 Dec 2018 13:20:07 +0000
Will Deacon <[email protected]> wrote:

> On Wed, Dec 05, 2018 at 12:48:54PM -0500, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <[email protected]>
> >
> > It has been reported that ftrace_replace_code() which is called by
> > ftrace_modify_all_code() can cause a soft lockup warning for an
> > allmodconfig kernel. This is because all the debug options enabled
> > causes the loop in ftrace_replace_code() (which loops over all the
> > functions being enabled where there can be 10s of thousands), is too
> > slow, and never schedules out.
> >
> > To solve this, setting FTRACE_SCHEDULABLE to the command passed into
> > ftrace_replace_code() will make it call cond_resched() in the loop,
> > which prevents the soft lockup warning from triggering.
> >
> > Link: http://lkml.kernel.org/r/[email protected]
> >
> > Reported-by: Anders Roxell <[email protected]>
> > Signed-off-by: Steven Rostedt (VMware) <[email protected]>
> > ---
> > arch/arm64/kernel/ftrace.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> > index 57e962290df3..9a8de0a79f97 100644
> > --- a/arch/arm64/kernel/ftrace.c
> > +++ b/arch/arm64/kernel/ftrace.c
> > @@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
> >
> > void arch_ftrace_update_code(int command)
> > {
> > + command |= FTRACE_SCHEDULABLE;
> > ftrace_modify_all_code(command);
> > }
>
> Bikeshed: I'd probably go for FTRACE_MAY_SLEEP, but I'm not going to die
> on that hill so...

I like bike sheds. Hmm, it's not too late to change this. Perhaps I
will.

>
> Acked-by: Will Deacon <[email protected]>

Thanks!

If I decide to change the name to MAY_SLEEP, I assume I can still keep
your Acked-by.

-- Steve

2018-12-06 16:08:13

by Will Deacon

Subject: Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

On Thu, Dec 06, 2018 at 10:59:14AM -0500, Steven Rostedt wrote:
> On Thu, 6 Dec 2018 13:20:07 +0000
> Will Deacon <[email protected]> wrote:
>
> > On Wed, Dec 05, 2018 at 12:48:54PM -0500, Steven Rostedt wrote:
> > > From: "Steven Rostedt (VMware)" <[email protected]>
> > >
> > > It has been reported that ftrace_replace_code() which is called by
> > > ftrace_modify_all_code() can cause a soft lockup warning for an
> > > allmodconfig kernel. This is because all the debug options enabled
> > > causes the loop in ftrace_replace_code() (which loops over all the
> > > functions being enabled where there can be 10s of thousands), is too
> > > slow, and never schedules out.
> > >
> > > To solve this, setting FTRACE_SCHEDULABLE to the command passed into
> > > ftrace_replace_code() will make it call cond_resched() in the loop,
> > > which prevents the soft lockup warning from triggering.
> > >
> > > Link: http://lkml.kernel.org/r/[email protected]
> > >
> > > Reported-by: Anders Roxell <[email protected]>
> > > Signed-off-by: Steven Rostedt (VMware) <[email protected]>
> > > ---
> > > arch/arm64/kernel/ftrace.c | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> > > index 57e962290df3..9a8de0a79f97 100644
> > > --- a/arch/arm64/kernel/ftrace.c
> > > +++ b/arch/arm64/kernel/ftrace.c
> > > @@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
> > >
> > > void arch_ftrace_update_code(int command)
> > > {
> > > + command |= FTRACE_SCHEDULABLE;
> > > ftrace_modify_all_code(command);
> > > }
> >
> > Bikeshed: I'd probably go for FTRACE_MAY_SLEEP, but I'm not going to die
> > on that hill so...
>
> I like bike sheds. Hmm, it's not too late to change this. Perhaps I
> will.
>
> >
> > Acked-by: Will Deacon <[email protected]>
>
> Thanks!
>
> If I decide to change the name to MAY_SLEEP, I assume I can still keep
> your Acked-by.

Of course!

Will