Messages in this thread Patch in this message | | | Date | Fri, 10 Oct 2008 01:44:44 -0400 | From | Mathieu Desnoyers <> | Subject | [PATCH] Markers : fix check format with rcu callback race |
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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.
* 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); -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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