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Diffstat (limited to '')
| -rw-r--r-- | Documentation/locking/locktypes.rst | 9 |
1 files changed, 3 insertions, 6 deletions
diff --git a/Documentation/locking/locktypes.rst b/Documentation/locking/locktypes.rst index ddada4a53749..4fd7b70fcde1 100644 --- a/Documentation/locking/locktypes.rst +++ b/Documentation/locking/locktypes.rst @@ -439,11 +439,9 @@ preemption. The following substitution works on both kernels:: spin_lock(&p->lock); p->count += this_cpu_read(var2); -On a non-PREEMPT_RT kernel migrate_disable() maps to preempt_disable() -which makes the above code fully equivalent. On a PREEMPT_RT kernel migrate_disable() ensures that the task is pinned on the current CPU which in turn guarantees that the per-CPU access to var1 and var2 are staying on -the same CPU. +the same CPU while the task remains preemptible. The migrate_disable() substitution is not valid for the following scenario:: @@ -456,9 +454,8 @@ scenario:: p = this_cpu_ptr(&var1); p->val = func2(); -While correct on a non-PREEMPT_RT kernel, this breaks on PREEMPT_RT because -here migrate_disable() does not protect against reentrancy from a -preempting task. A correct substitution for this case is:: +This breaks because migrate_disable() does not protect against reentrancy from +a preempting task. A correct substitution for this case is:: func() { |