lkml.org 
[lkml]   [2013]   [Mar]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] tracepoints: prevents null probe from being added
* Steven Rostedt (rostedt@goodmis.org) wrote:
> On Wed, 2013-03-20 at 12:18 +0900, kpark3469@gmail.com wrote:
> > From: Sahara <keun-o.park@windriver.com>
> >
> > Somehow tracepoint_entry_add/remove_probe functions allow a null probe
> > function.
>
> You actually hit this in practice, or is this just something that you
> observe from code review?
>
> > Especially on getting a null probe in remove function, it seems
> > to be used to remove all probe functions in the entry.
>
> Hmm, that actually sounds like a feature.

Yep. It's been a long time since I wrote this code, but the removal code
seems to use NULL probe pointer to remove all probes for a given
tracepoint.

I'd be tempted to just validate non-NULL probe within
tracepoint_entry_add_probe() and let other sites as is, just in case
anyone would be using this feature.

I cannot say that I have personally used this "remove all" feature much
though.

Thanks,

Mathieu

>
> > But, the code is not handled as expected. Since the tracepoint_entry
> > maintains funcs array's last func as NULL in order to mark it as the end
> > of the array. Also NULL func is used in for-loop to check out the end of
> > the loop. So if there's NULL func in the entry's funcs, the for-loop
> > will be abruptly ended in the middle of operation.
> > Also checking out if probe is null in for-loop is not efficient.
> >
> > Signed-off-by: Sahara <keun-o.park@windriver.com>
> > ---
> > kernel/tracepoint.c | 18 ++++++++++++------
> > 1 files changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> > index 0c05a45..30f427e 100644
> > --- a/kernel/tracepoint.c
> > +++ b/kernel/tracepoint.c
> > @@ -112,7 +112,10 @@ tracepoint_entry_add_probe(struct tracepoint_entry *entry,
> > int nr_probes = 0;
> > struct tracepoint_func *old, *new;
> >
> > - WARN_ON(!probe);
> > + if (unlikely(!probe)) {
> > + WARN_ON(!probe);
> > + return ERR_PTR(-EINVAL);
> > + }
>
> Um, you want:
>
> if (WARN_ON(!probe))
> return ERR_PTR(-EINVAL);
>
> >
> > debug_print_probes(entry);
> > old = entry->funcs;
> > @@ -147,15 +150,19 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
> >
> > old = entry->funcs;
> >
> > + if (unlikely(!probe)) {
> > + WARN_ON(!probe);
> > + return ERR_PTR(-EINVAL);
> > + }
>
> Here too if it wasn't intended to allow removal of all probes from a
> tracepoint.
>
> > +
> > if (!old)
> > return ERR_PTR(-ENOENT);
> >
> > debug_print_probes(entry);
> > /* (N -> M), (N > 1, M >= 0) probes */
> > for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> > - if (!probe ||
> > - (old[nr_probes].func == probe &&
> > - old[nr_probes].data == data))
> > + if (old[nr_probes].func == probe &&
> > + old[nr_probes].data == data)
> > nr_del++;
> > }
> >
> > @@ -173,8 +180,7 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
> > if (new == NULL)
> > return ERR_PTR(-ENOMEM);
> > for (i = 0; old[i].func; i++)
> > - if (probe &&
> > - (old[i].func != probe || old[i].data != data))
> > + if (old[i].func != probe || old[i].data != data)
>
> This makes it look like the null probe was intentional.
>
> -- Steve
>
> > new[j++] = old[i];
> > new[nr_probes - nr_del].func = NULL;
> > entry->refcount = nr_probes - nr_del;
>
>

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com


\
 
 \ /
  Last update: 2013-03-20 19:41    [W:0.058 / U:0.780 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site