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From: Artem Bityutskiy on 21 Jul 2010 05:40
From: Artem Bityutskiy <Artem.Bityutskiy(a)nokia.com>

Currently, if someone submits jobs for the default bdi, we can lose wake-up
events. E.g., this can happen if 'bdi_queue_work()' is called when
'bdi_forker_thread()' is executing code after 'wb_do_writeback(me, 0)', but
before 'set_current_state(TASK_INTERRUPTIBLE)'.

This situation is unlikely, and the result is not very severe - we'll just
delay the execution of the work, but this is still not very nice.

This patch fixes the issue by checking whether the default bdi has works before
the forker thread goes sleep.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy(a)nokia.com>
---
mm/backing-dev.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 0ea5e4c..ae44417 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -358,6 +358,10 @@ static int bdi_forker_thread(void *ptr)
bdi_add_default_flusher_thread(bdi);
}

+ /* Keep working if default bdi still has things to do */
+ if (!list_empty(&me->bdi->work_list))
+ __set_current_state(TASK_RUNNING);
+
if (list_empty(&bdi_pending_list)) {
unsigned long wait;

--
1.7.1.1

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Prev: [PATCHv2 08/11] writeback: move last_active to bdi
Next: [PATCHv2 00/16] kill unnecessary bdi wakeups + cleanups