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authorPaul E. McKenney <paul.mckenney@linaro.org>2012-01-23 12:41:26 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-02-21 09:06:03 -0800
commitc0d6d01bffdce19fa19baad6cb8cc3eed7bfd6f5 (patch)
treeea4c20ddc87b94d7bef2402fe6dbe3186be263c2 /kernel/rcupdate.c
parent24cd7fd0eaa0d9f5e197ff77a83b006a86696068 (diff)
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rcu: Check for illegal use of RCU from offlined CPUs
Although it is legal to use RCU during early boot, it is anything but legal to use RCU at runtime from an offlined CPU. After all, RCU explicitly ignores offlined CPUs. This commit therefore adds checks for runtime use of RCU from offlined CPUs. These checks are not perfect, in particular, they can be subverted through use of things like rcu_dereference_raw(). Note that it is not possible to put checks in rcu_read_lock() and friends due to the fact that these primitives are used in code that might be used under either RCU or lock-based protection, which means that checking rcu_read_lock() gets you fat piles of false positives. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcupdate.c')
-rw-r--r--kernel/rcupdate.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 2bc4e13..a86f174 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -88,6 +88,9 @@ EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
* section.
*
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
+ *
+ * Note that rcu_read_lock() is disallowed if the CPU is either idle or
+ * offline from an RCU perspective, so check for those as well.
*/
int rcu_read_lock_bh_held(void)
{
@@ -95,6 +98,8 @@ int rcu_read_lock_bh_held(void)
return 1;
if (rcu_is_cpu_idle())
return 0;
+ if (!rcu_lockdep_current_cpu_online())
+ return 0;
return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
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