Hi Yunlei,
> -----Original Message-----
> From: He YunLei [mailto:heyun...@huawei.com]
> Sent: Tuesday, February 23, 2016 7:36 PM
> To: Chao Yu; jaeg...@kernel.org; linux-f2fs-devel@lists.sourceforge.net
> Cc: bintian.w...@huawei.com; 'Biao He'
> Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid hungtask problem caused by losing
> wake_up
>
> On 2016/2/23 17:15, Chao Yu wrote:
> Hi Chao,
>
> > Hi Yunlei,
> >
> >> -----Original Message-----
> >> From: He YunLei [mailto:heyun...@huawei.com]
> >> Sent: Tuesday, February 23, 2016 3:03 PM
> >> To: Chao Yu; jaeg...@kernel.org; linux-f2fs-devel@lists.sourceforge.net
> >> Cc: bintian.w...@huawei.com; 'Biao He'
> >> Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid hungtask problem caused by
> >> losing wake_up
> >>
> >> On 2016/2/23 13:44, Chao Yu wrote:
> >>> Hi Yunlei,
> >> Hi Chao,
> >>>
> >>>> -----Original Message-----
> >>>> From: Yunlei He [mailto:heyun...@huawei.com]
> >>>> Sent: Tuesday, February 23, 2016 12:08 PM
> >>>> To: chao2...@samsung.com; jaeg...@kernel.org;
> >>>> linux-f2fs-devel@lists.sourceforge.net
> >>>> Cc: bintian.w...@huawei.com; Yunlei He; Biao He
> >>>> Subject: [f2fs-dev] [PATCH] f2fs: avoid hungtask problem caused by
> >>>> losing wake_up
> >>>>
> >>>> The D state of wait_on_all_pages_writeback should be waken by
> >>>> function f2fs_write_end_io when all writeback pages have been
> >>>> succesfully written to device. It's possible that wake_up comes
> >>>> between get_pages and io_schedule. Maybe in this case it will
> >>>> lost wake_up and still in D state even if all pages have been
> >>>> write back to device, and finally, the whole system will be into
> >>>> the hungtask state.
> >>>
> >>> I haven't encountered such issue so far, do you suffer this in real
> >>> world?
> >>>
> >> yes, I have encounter it, the whole file system is blocked at function
> >> wait_on_all_pages_writeback beyond 120s when write cp, and no error
> >> reported
> >> by storage device driver.
> >
> > Could this reproducible? If it could, could you please share the details.
> > And did this occur in a huge size f2fs image?
> >
> >>>>
> >>>> if (!get_pages(sbi, F2FS_WRITEBACK))
> >>>> break;
> >>>> <--------- wake_up
> >>>
> >>> wake_up will put all tasks linked in sbi->cp_wait on run-queue, so
> >>> here it should be save to call io_schedule, after being rescheduled,
> >>> it will get the chance to check above condition to break out.
> >>>
> >>> Thanks,
> >>
> >> Here, we just doubt something weird may cause wait_on_all_pages_writeback
> >> could not be waken. Wake_up trigger only one time by last bio's end_io
> >> function, if the thread happen to miss it, the thread will be in D state
> >> forever. So we change the code to make wait_on_all_pages_writeback awaken
> >> periodically, then check the condition.
> >
> > Got it.
> >
> > The patch can fix issue that checkpointer will wait forever in case of
> > write_end_io was failed to call wake_up for some reason.
I found one possible case:
CPU0: CPU1:
- write_checkpoint
- do_checkpoint
- wait_on_all_pages_writeback
- f2fs_write_end_io
- wake_up
this is last writebacked page, but
no sleeper in sbi->cp_wait wait
queue, wake_up is not been called.
- prepare_to_wait(TASK_UNINTERRUPTIBLE)
Here, current task is been preempted,
but there will be no waker to wake up
this task since last write_end_io
has been called before. So current
task will sleep forever.
- io_schedule
How do you think of it?
And if this is right, following patch can fix this issue.
---
fs/f2fs/checkpoint.c | 14 +++++++++-----
fs/f2fs/data.c | 9 +++++++--
fs/f2fs/f2fs.h | 3 ++-
fs/f2fs/super.c | 1 +
4 files changed, 19 insertions(+), 8 deletions(-)
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 9d277f8..9446c3d 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -914,15 +914,19 @@ static void wait_on_all_pages_writeback(struct
f2fs_sb_info *sbi)
{
DEFINE_WAIT(wait);
- for (;;) {
- prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
+ spin_lock(&sbi->cp_wb_lock);
- if (!get_pages(sbi, F2FS_WRITEBACK))
- break;
+ while (get_pages(sbi, F2FS_WRITEBACK)) {
+ prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
+ spin_unlock(&sbi->cp_wb_lock);
io_schedule();
+ spin_lock(&sbi->cp_wb_lock);
+
+ finish_wait(&sbi->cp_wait, &wait);
}
- finish_wait(&sbi->cp_wait, &wait);
+
+ spin_unlock(&sbi->cp_wb_lock);
}
static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index e5c762b..e31deb97 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -59,6 +59,7 @@ static void f2fs_write_end_io(struct bio *bio)
{
struct f2fs_sb_info *sbi = bio->bi_private;
struct bio_vec *bvec;
+ unsigned long flags;
int i;
bio_for_each_segment_all(bvec, bio, i) {
@@ -74,8 +75,12 @@ static void f2fs_write_end_io(struct bio *bio)
dec_page_count(sbi, F2FS_WRITEBACK);
}
- if (!get_pages(sbi, F2FS_WRITEBACK) && wq_has_sleeper(&sbi->cp_wait))
- wake_up(&sbi->cp_wait);
+ if (!get_pages(sbi, F2FS_WRITEBACK)) {
+ spin_lock_irqsave(&sbi->cp_wb_lock, flags);
+ if (wq_has_sleeper(&sbi->cp_wait))
+ wake_up(&sbi->cp_wait);
+ spin_unlock_irqrestore(&sbi->cp_wb_lock, flags);
+ }
bio_put(bio);
}
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 0d25430..fd47984 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -727,7 +727,8 @@ struct f2fs_sb_info {
struct rw_semaphore cp_rwsem; /* blocking FS operations */
struct rw_semaphore node_write; /* locking node writes */
struct mutex writepages; /* mutex for writepages() */
- wait_queue_head_t cp_wait;
+ wait_queue_head_t cp_wait; /* for wait pages writeback */
+ spinlock_t cp_wb_lock; /* for protect cp_wait */
unsigned long last_time[MAX_TIME]; /* to store time in jiffies */
long interval_time[MAX_TIME]; /* to store thresholds */
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 7b62016..5316c7a 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1374,6 +1374,7 @@ try_onemore:
init_rwsem(&sbi->cp_rwsem);
init_waitqueue_head(&sbi->cp_wait);
+ spin_lock_init(&sbi->cp_wb_lock);
init_sb_info(sbi);
/* get an inode for meta space */
--
2.7.0
> >
> > But I doubt more that the reason we are stuck is there are remained pages
> > cached in bio buffer without being submitted. To make sure, maybe in
> > wait_on_all_pages_writeback we could add print info to see whether
> > sbi->write_io[].bio is valid or not.
> >
> We use tool dump f2fs_sb_info information and find that:
>
> write_io[DATA].bio = 0;
> write_io[NODE].bio = 0;
> write_io[META].bio = 0;
>
> nr_pages[F2FS_WRITEBACK] = 0;
> nr_pages[F2FS_DIRTY_DENTS] = 0;
> nr_pages[F2FS_DIRTY_NODES] = 13;
Weird, dirty nodes count should be 0.
Thanks
> nr_pages[F2FS_DIRTY_META] = 0;
> nr_pages[F2FS_INMEM_PAGES] = 0;
>
> So we believe that the block device is ok!
>
> Thanks,
>
> > Thanks,
> >
> >>
> >>>
> >>>> io_schedule();
> >>>>
> >>>> Signed-off-by: Yunlei He <heyun...@huawei.com>
> >>>> Signed-off-by: Biao He <hebi...@huawei.com>
> >>>> ---
> >>>> fs/f2fs/checkpoint.c | 2 +-
> >>>> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>>> index 2bac8a1..f55355d 100644
> >>>> --- a/fs/f2fs/checkpoint.c
> >>>> +++ b/fs/f2fs/checkpoint.c
> >>>> @@ -920,7 +920,7 @@ static void wait_on_all_pages_writeback(struct
> >>>> f2fs_sb_info *sbi)
> >>>> if (!get_pages(sbi, F2FS_WRITEBACK))
> >>>> break;
> >>>>
> >>>> - io_schedule();
> >>>> + io_schedule_timeout(5*HZ);
> >>>> }
> >>>> finish_wait(&sbi->cp_wait, &wait);
> >>>> }
> >>>> --
> >>>> 1.9.1
> >>>
> >>>
> >>>
> >>> .
> >>>
> >
> >
> >
> > .
> >
------------------------------------------------------------------------------
Site24x7 APM Insight: Get Deep Visibility into Application Performance
APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month
Monitor end-to-end web transactions and take corrective actions now
Troubleshoot faster and improve end-user experience. Signup Now!
http://pubads.g.doubleclick.net/gampad/clk?id=272487151&iu=/4140
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
