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Subject[PATCH v2] mm: Make logic in bdi_forker_thread() straight
Date
The logic in bdi_forker_thread() is unnecessarily convoluted by setting task
state there and back or calling schedule_timeout() in TASK_RUNNING state. Also
clearing of BDI_pending bit is placed at the and of global loop and cases of a
switch which mustn't reach it must call 'continue' instead of 'break' which is
non-intuitive and thus asking for trouble. So make the logic more obvious.

CC: Andrew Morton <akpm@linux-foundation.org>
CC: Wu Fengguang <fengguang.wu@intel.com>
CC: consul.kautuk@gmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
mm/backing-dev.c | 37 ++++++++++++++++++++-----------------
1 files changed, 20 insertions(+), 17 deletions(-)
This should be the right cleanup. Jens?

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index d6edf8d..bdf7d6b 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -359,6 +359,17 @@ static unsigned long bdi_longest_inactive(void)
return max(5UL * 60 * HZ, interval);
}

+/*
+ * Clear pending bit and wakeup anybody waiting for flusher thread startup
+ * or teardown.
+ */
+static void bdi_clear_pending(struct backing_dev_info *bdi)
+{
+ clear_bit(BDI_pending, &bdi->state);
+ smp_mb__after_clear_bit();
+ wake_up_bit(&bdi->state, BDI_pending);
+}
+
static int bdi_forker_thread(void *ptr)
{
struct bdi_writeback *me = ptr;
@@ -390,8 +401,6 @@ static int bdi_forker_thread(void *ptr)
}

spin_lock_bh(&bdi_lock);
- set_current_state(TASK_INTERRUPTIBLE);
-
list_for_each_entry(bdi, &bdi_list, bdi_list) {
bool have_dirty_io;

@@ -441,13 +450,8 @@ static int bdi_forker_thread(void *ptr)
}
spin_unlock_bh(&bdi_lock);

- /* Keep working if default bdi still has things to do */
- if (!list_empty(&me->bdi->work_list))
- __set_current_state(TASK_RUNNING);
-
switch (action) {
case FORK_THREAD:
- __set_current_state(TASK_RUNNING);
task = kthread_create(bdi_writeback_thread, &bdi->wb,
"flush-%s", dev_name(bdi->dev));
if (IS_ERR(task)) {
@@ -469,14 +473,21 @@ static int bdi_forker_thread(void *ptr)
spin_unlock_bh(&bdi->wb_lock);
wake_up_process(task);
}
+ bdi_clear_pending(bdi);
break;

case KILL_THREAD:
- __set_current_state(TASK_RUNNING);
kthread_stop(task);
+ bdi_clear_pending(bdi);
break;

case NO_ACTION:
+ /* Keep working if default bdi still has things to do */
+ if (!list_empty(&me->bdi->work_list)) {
+ try_to_freeze();
+ break;
+ }
+ set_current_state(TASK_INTERRUPTIBLE);
if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
/*
* There are no dirty data. The only thing we
@@ -489,16 +500,8 @@ static int bdi_forker_thread(void *ptr)
else
schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
try_to_freeze();
- /* Back to the main loop */
- continue;
+ break;
}
-
- /*
- * Clear pending bit and wakeup anybody waiting to tear us down.
- */
- clear_bit(BDI_pending, &bdi->state);
- smp_mb__after_clear_bit();
- wake_up_bit(&bdi->state, BDI_pending);
}

return 0;
--
1.7.1


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