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SubjectRe: [PATCH] Markers : fix check format with rcu callback race
Mathieu Desnoyers wrote:
> The fix "markers: fix unchecked format" introduced an RCU callback race. This
> patch takes care of calling any pending RCU callback before set_format is
> called.
>

marker_set_format() has this statement:

if ((*entry)->rcu_pending)
rcu_barrier_sched();

>
> * Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
>> bit-field is not thread-safe nor smp-safe.
>>
>> struct marker_entry.rcu_pending is not protected by any lock
>> in rcu-callback free_old_closure().
>> so we must turn it into a safe type.
>>
>
> All struct marker_entry.rcu_pending accesses are done with the
> markers_mutex held, except the one done in free_old_closure(). Normally,
> there should be a
> if (entry->rcu_pending)
> rcu_barrier_sched();
>
> At the beginning of each markers_mutex section (just after get_marker())
> to make sure any pending callback is executed at that point before any
> of rcu_pending or ptype are touched.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> CC: Ingo Molnar <mingo@elte.hu>
> CC: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> kernel/marker.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> Index: linux-2.6-lttng/kernel/marker.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/marker.c 2008-10-10 01:35:32.000000000 -0400
> +++ linux-2.6-lttng/kernel/marker.c 2008-10-10 01:35:32.000000000 -0400
> @@ -657,21 +657,23 @@ int marker_probe_register(const char *na
> entry = add_marker(name, format);
> if (IS_ERR(entry))
> ret = PTR_ERR(entry);
> - } else if (format) {
> - if (!entry->format)
> - ret = marker_set_format(&entry, format);
> - else if (strcmp(entry->format, format))
> - ret = -EPERM;
> + } else {
> + /*
> + * If we detect that a call_rcu is pending for this marker,
> + * make sure it's executed now.
> + */
> + if (entry->rcu_pending)
> + rcu_barrier_sched();
> + if (format) {
> + if (!entry->format)
> + ret = marker_set_format(&entry, format);
> + else if (strcmp(entry->format, format))
> + ret = -EPERM;
> + }
> }
> if (ret)
> goto end;
>
> - /*
> - * If we detect that a call_rcu is pending for this marker,
> - * make sure it's executed now.
> - */
> - if (entry->rcu_pending)
> - rcu_barrier_sched();
> old = marker_entry_add_probe(entry, probe, probe_private);
> if (IS_ERR(old)) {
> ret = PTR_ERR(old);




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