On 12/17/2019 6:01 PM, James Bottomley wrote:
This code is confusing me:
+ /*
+ * To avoid holding the mutex when processing queued keys,
+ * transfer the queued keys with the mutex held to a temp list,
+ * release the mutex, and then process the queued keys from
+ * the temp list.
+ *
+ * Since ima_process_keys is set to true, any new key will be
+ * processed immediately and not be queued.
+ */
+ INIT_LIST_HEAD(&temp_ima_keys);
+
+ mutex_lock(&ima_keys_mutex);
+
+ if (!ima_process_keys) {
+ ima_process_keys = true;
+
+ if (!list_empty(&ima_keys)) {
+ list_for_each_entry_safe(entry, tmp, &ima_keys, list)
+ list_move_tail(&entry->list, &temp_ima_keys);
+ process = true;
+ }
+ }
+
+ mutex_unlock(&ima_keys_mutex);
+
The direct implication of the comment and the lock dance with the
temporary list and the processed flag is that stuff can be added to the
ima_keys list after you drop the mutex. Your explanation in the prior
couple of emails says that nothing can be added because the
ima_process_keys flag setting prevents it. If the latter is true, you
can simply drop the lock after setting the flag and rely on ima_keys
not changing to run it through process_buffer_measurement without
needing any of the intermediate list or the processed flag. If the
latter isn't true then any key added to ima_keys after the mutex is
dropped is never processed.
James
Once the flag is set no new key will be added to ima_keys list.
You are right - if the flag is set with the lock taken, then there is no
need for the temp list. After dropping the lock, measurement can be done
directly from ima_keys list.
Thanks for reviewing the code. I'll send an update tomorrow.
-lakshmi
