So,
…snip…
+static int ksm_seeker_thread(void *nothing)
+{
+ pid_t last_pid = 1;
+ pid_t curr_pid;
+ struct task_struct *task;
+
+ set_freezable();
+ set_user_nice(current, 5);
+
+ while (!kthread_should_stop()) {
+ wait_while_offlining();
+
+ try_to_freeze();
+
+ if (!ksm_mode_always()) {
+ wait_event_freezable(ksm_seeker_thread_wait,
+ ksm_mode_always() || kthread_should_stop());
+ continue;
+ }
+
+ /*
+ * import one task's vma per run
+ */
+ read_lock(&tasklist_lock);
+
+ /* Try always get next task */
+ for_each_process(task) {
+ curr_pid = task_pid_nr(task);
+ if (curr_pid == last_pid) {
+ task = next_task(task);
+ break;
+ }
+
+ if (curr_pid > last_pid)
+ break;
+ }
+
+ last_pid = task_pid_nr(task);
+ ksm_import_task_vma(task);
This seems to be a bad idea. ksm_import_task_vma() may sleep with
tasklist_lock being held. Thus, IIUC, you'll get this:
[ 1754.410322] BUG: scheduling while atomic: ksmd_seeker/50/0x00000002
…
[ 1754.410444] Call Trace:
[ 1754.410455] dump_stack+0x5c/0x80
[ 1754.410460] __schedule_bug.cold.19+0x38/0x51
[ 1754.410464] __schedule+0x11dc/0x2080
[ 1754.410483] schedule+0x32/0xb0
[ 1754.410487] rwsem_down_write_failed+0x15d/0x240
[ 1754.410496] call_rwsem_down_write_failed+0x13/0x20
[ 1754.410499] down_write+0x20/0x30
[ 1754.410502] ksm_import_task_vma+0x22/0x70
[ 1754.410505] ksm_seeker_thread+0x134/0x1c0
[ 1754.410512] kthread+0x113/0x130
[ 1754.410518] ret_from_fork+0x35/0x40
I think you may want to get a reference to task_struct before releasing
tasklist_lock, and then put it after ksm_import_task_vma() does its job.
+ read_unlock(&tasklist_lock);
+
+ schedule_timeout_interruptible(
+ msecs_to_jiffies(ksm_thread_seeker_sleep_millisecs));
+ }
+ return 0;
+}
…snip…
--
Oleksandr Natalenko (post-factum)
