[PATCH] plug preempt leak in _stp_runtime_entryfn_put/get_context

[PATCH] plug preempt leak in _stp_runtime_entryfn_put/get_context

[Mateusz Guzik]

If _stp_runtime_entryfn_get_context returns a context, preemption
counter is always incremented. On the other hand
_stp_runtime_entryfn_put_context only decrements the counter if the
passed context matches the one currently set on the cpu.

The context can be set to NULL by _stp_runtime_contexts_free, making the
comparison false and in effect leading to a leak, e.g.:
timer: _stp_ctl_work_callback+0x0/0x1e0[stap_af8544c7eb51251ef8c
 377abff659b05_25070] preempt leak: 00000101 -> 00000102

Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
---
 runtime/linux/runtime_context.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/runtime/linux/runtime_context.h b/runtime/linux/runtime_context.h
index c9ffe18..9d325da 100644
--- a/runtime/linux/runtime_context.h
+++ b/runtime/linux/runtime_context.h
@@ -80,11 +80,12 @@ static struct context * _stp_runtime_entryfn_get_context(void)
 
 static inline void _stp_runtime_entryfn_put_context(struct context *c)
 {
-	if (c && c == _stp_runtime_get_context()) {
-		atomic_dec(&c->busy);
+	if (c) {
+		if (c == _stp_runtime_get_context())
+			atomic_dec(&c->busy);
+		/* else, warn about bad state? */
 		preempt_enable_no_resched();
 	}
-	/* else, warn about bad state? */
 	return;
 }
 
-- 
2.5.5

Re: [PATCH] plug preempt leak in _stp_runtime_entryfn_put/get_context

[David Smith]

On 05/02/2016 10:48 AM, Mateusz Guzik wrote:
> If _stp_runtime_entryfn_get_context returns a context, preemption
> counter is always incremented. On the other hand
> _stp_runtime_entryfn_put_context only decrements the counter if the
> passed context matches the one currently set on the cpu.
> 
> The context can be set to NULL by _stp_runtime_contexts_free, making the
> comparison false and in effect leading to a leak, e.g.:
> timer: _stp_ctl_work_callback+0x0/0x1e0[stap_af8544c7eb51251ef8c
>  377abff659b05_25070] preempt leak: 00000101 -> 00000102
> 
> Signed-off-by: Mateusz Guzik <mguzik@redhat.com>

I checked this in. Thanks for the patch!

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
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