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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-11-06 23:05:32 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-12-05 12:34:32 -0800 |
| commit | c64c4b0f9a183e4c73abff848378afa6edf796c5 (patch) | |
| tree | bd0fa2e58b367e35dae47101ebd0de4b28642e9c /Documentation/RCU | |
| parent | 4b689330b1a5858e88831b3752e9a6692a5c7bdb (diff) | |
| download | linux-next-c64c4b0f9a183e4c73abff848378afa6edf796c5.tar.gz | |
documentation: Update RCU requirements based on expedited changes
Because RCU-sched expedited grace periods now use IPIs and interact
with rcu_read_unlock(), it is no longer sufficient to disable preemption
across RCU read-side critical sections that acquire and hold scheduler
locks. It is now necessary to instead disable interrupts. This commit
documents this change.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.html | 12 | ||||
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.htmlx | 10 |
2 files changed, 19 insertions, 3 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 96cdcf7195d5..a725f9900ec8 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -1,5 +1,5 @@ <!-- DO NOT HAND EDIT. --> -<!-- Instead, edit Requirements.htmlx and run 'sh htmlqqz.sh Requirements' --> +<!-- Instead, edit Documentation/RCU/Design/Requirements/Requirements.htmlx and run 'sh htmlqqz.sh Documentation/RCU/Design/Requirements/Requirements' --> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> @@ -1957,7 +1957,7 @@ 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. @@ -1966,6 +1966,14 @@ 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 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 |