* ftrace_direct_func_count ?
@ 2024-05-04 13:35 Dr. David Alan Gilbert
2024-05-06 17:25 ` Steven Rostedt
0 siblings, 1 reply; 3+ messages in thread
From: Dr. David Alan Gilbert @ 2024-05-04 13:35 UTC (permalink / raw
To: linux-trace-kernel, rostedt
Hi,
I've just posted a patch 'ftrace: Remove unused list 'ftrace_direct_funcs''
that clears out some old code, but while at it I noticed the global
'ftrace_direct_func_count'.
As far as I can tell, it's never assigned (or initialised) but it is tested:
kernel/trace/fgraph.c:
#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
/*
* Skip graph tracing if the return location is served by direct trampoline,
* since call sequence and return addresses are unpredictable anyway.
* Ex: BPF trampoline may call original function and may skip frame
* depending on type of BPF programs attached.
*/
if (ftrace_direct_func_count &&
ftrace_find_rec_direct(ret - MCOUNT_INSN_SIZE))
return -EBUSY;
#endif
So I wasn't sure whether it was just safe to nuke that section
or whether it really needed fixing?
Dave
--
-----Open up your eyes, open up your mind, open up your code -------
/ Dr. David Alan Gilbert | Running GNU/Linux | Happy \
\ dave @ treblig.org | | In Hex /
\ _________________________|_____ http://www.treblig.org |_______/
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: ftrace_direct_func_count ?
2024-05-04 13:35 ftrace_direct_func_count ? Dr. David Alan Gilbert
@ 2024-05-06 17:25 ` Steven Rostedt
2024-05-06 17:26 ` Dr. David Alan Gilbert
0 siblings, 1 reply; 3+ messages in thread
From: Steven Rostedt @ 2024-05-06 17:25 UTC (permalink / raw
To: Dr. David Alan Gilbert; +Cc: linux-trace-kernel
On Sat, 4 May 2024 13:35:26 +0000
"Dr. David Alan Gilbert" <dave@treblig.org> wrote:
> Hi,
> I've just posted a patch 'ftrace: Remove unused list 'ftrace_direct_funcs''
> that clears out some old code, but while at it I noticed the global
> 'ftrace_direct_func_count'.
>
> As far as I can tell, it's never assigned (or initialised) but it is tested:
>
> kernel/trace/fgraph.c:
> #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> /*
> * Skip graph tracing if the return location is served by direct trampoline,
> * since call sequence and return addresses are unpredictable anyway.
> * Ex: BPF trampoline may call original function and may skip frame
> * depending on type of BPF programs attached.
> */
> if (ftrace_direct_func_count &&
> ftrace_find_rec_direct(ret - MCOUNT_INSN_SIZE))
> return -EBUSY;
> #endif
>
> So I wasn't sure whether it was just safe to nuke that section
> or whether it really needed fixing?
Yes, after commit 8788ca164eb4bad ("ftrace: Remove the legacy
_ftrace_direct API") that variable is no longer used.
-- Steve
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: ftrace_direct_func_count ?
2024-05-06 17:25 ` Steven Rostedt
@ 2024-05-06 17:26 ` Dr. David Alan Gilbert
0 siblings, 0 replies; 3+ messages in thread
From: Dr. David Alan Gilbert @ 2024-05-06 17:26 UTC (permalink / raw
To: Steven Rostedt; +Cc: linux-trace-kernel
* Steven Rostedt (rostedt@goodmis.org) wrote:
> On Sat, 4 May 2024 13:35:26 +0000
> "Dr. David Alan Gilbert" <dave@treblig.org> wrote:
>
> > Hi,
> > I've just posted a patch 'ftrace: Remove unused list 'ftrace_direct_funcs''
> > that clears out some old code, but while at it I noticed the global
> > 'ftrace_direct_func_count'.
> >
> > As far as I can tell, it's never assigned (or initialised) but it is tested:
> >
> > kernel/trace/fgraph.c:
> > #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> > /*
> > * Skip graph tracing if the return location is served by direct trampoline,
> > * since call sequence and return addresses are unpredictable anyway.
> > * Ex: BPF trampoline may call original function and may skip frame
> > * depending on type of BPF programs attached.
> > */
> > if (ftrace_direct_func_count &&
> > ftrace_find_rec_direct(ret - MCOUNT_INSN_SIZE))
> > return -EBUSY;
> > #endif
> >
> > So I wasn't sure whether it was just safe to nuke that section
> > or whether it really needed fixing?
>
> Yes, after commit 8788ca164eb4bad ("ftrace: Remove the legacy
> _ftrace_direct API") that variable is no longer used.
OK, thanks, I'll send a follow up patch to my other patch to nuke
this as well.
Dave
> -- Steve
--
-----Open up your eyes, open up your mind, open up your code -------
/ Dr. David Alan Gilbert | Running GNU/Linux | Happy \
\ dave @ treblig.org | | In Hex /
\ _________________________|_____ http://www.treblig.org |_______/
^ permalink raw reply [flat|nested] 3+ messages in thread
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