On 04/01/2018 1:09 AM, Michael Lyle wrote:

On 01/03/2018 06:03 AM, Coly Li wrote:

quoted

Kernel thread routine bch_allocator_thread() references macro
allocator_wait() to wait for a condition or quit to do_exit()
when kthread_should_stop() is true.

Macro allocator_wait() has 2 issues in setting task state, let's
see its code piece,

284         while (1) {                                                   \
285                 set_current_state(TASK_INTERRUPTIBLE);                \
286                 if (cond)                                             \
287                         break;                                        \
288                                                                       \
289                 mutex_unlock(&(ca)->set->bucket_lock);                \
290                 if (kthread_should_stop())                            \
291                         return 0;                                     \
292                                                                       \
293                 schedule();                                           \
294                 mutex_lock(&(ca)->set->bucket_lock);                  \
295         }                                                             \
296         __set_current_state(TASK_RUNNING);                            \

1) At line 285, task state is set to TASK_INTERRUPTIBLE, if at line 290
kthread_should_stop() is true, the kernel thread will terminate and return
to kernel/kthread.s:kthread(), then calls do_exit() with TASK_INTERRUPTIBLE
state. This is not a suggested behavior and a warning message will be
reported by might_sleep() in do_exit() code path: "WARNING: do not call
blocking ops when !TASK_RUNNING; state=1 set at [xxxx]".

2) Because task state is set to TASK_INTERRUPTIBLE at line 285, when break
while-loop the task state has to be set back to TASK_RUNNING at line 296.
Indeed it is unncessary, if task state is set to TASK_INTERRUPTIBLE before
calling schedule() at line 293, we don't need to set the state back to
TASK_RUNNING at line 296 anymore. The reason is, allocator kthread is only
woken up by wake_up_process(), this routine makes sure the task state of
allocator kthread will be TASK_RUNNING after it returns from schedule() at
line 294 (see kernel/sched/core.c:try_to_wake_up() for more detailed
information).

This patch fixes the above 2 issues by,
1) Setting TASK_INTERRUPTIBLE state just before calling schedule().
2) Then setting TASK_RUNNING at line 296 is unnecessary, remove it.

Signed-off-by: Coly Li <redacted>

Hi Mike,

I also feel I made mistake here. set_current_state(TASK_INTERRUPTIBLE)
must be called before the condition check, other wise there will be a
race window on task state setting. A correct fix should be setting task
state to TASK_RUNNING before calling 'return 0', or before calling
mutex_unlock(&(ca)->set->bucket_lock).

When I review the new closure_sync() patches, I feel I make mistake
here. It will be fixed in v2 patch set.

Thanks.

Coly Li