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Diffstat (limited to 'Documentation/RCU/Design/Requirements/Requirements.htmlx')
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.htmlx | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.htmlx b/Documentation/RCU/Design/Requirements/Requirements.htmlx index 2d0cd90987f6..3a97ba490c42 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.htmlx +++ b/Documentation/RCU/Design/Requirements/Requirements.htmlx @@ -2124,7 +2124,7 @@ the runqueue locks and the priority-inheritance locks in the middle of an outermost RCU read-side critical section unless either (1) it releases them before exiting that same RCU read-side critical section, or -(2) preemption is disabled across +(2) interrupts are disabled across that entire RCU read-side critical section. This same prohibition also applies (recursively!) to any lock that is acquired while holding any lock to which this prohibition applies. @@ -2133,6 +2133,14 @@ Adhering to this rule prevents preemptible RCU from invoking priority-inheritance locks are held, thus avoiding deadlock. <p> +Prior to v4.4, it was only necessary to disable preemption across +RCU read-side critical sections that acquired scheduler locks. +In v4.4, expedited grace periods started using IPIs, and these +IPIs could force a <tt>rcu_read_unlock()</tt> to take the slowpath. +Therefore, this expedited-grace-period change required disabling of +interrupts, not just preemption. + +<p> For RCU's part, the preemptible-RCU <tt>rcu_read_unlock()</tt> implementation must be written carefully to avoid similar deadlocks. In particular, <tt>rcu_read_unlock()</tt> must tolerate an |