* [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
@ 2016-04-27 13:41 Chao Yu
2016-04-27 18:09 ` Jaegeuk Kim
0 siblings, 1 reply; 7+ messages in thread
From: Chao Yu @ 2016-04-27 13:41 UTC (permalink / raw)
To: Jaegeuk Kim, linux-f2fs-devel, linux-kernel
From: Chao Yu <yuchao0@huawei.com>
The following condition can happen in a preemptible kernel, it may cause
checkpointer hunging.
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 can been preempted,
but there will be no waker since last
write_end_io has bypassed wake_up. So
current task will sleep forever.
- io_schedule_timeout
Now we use spinlock to create a critical section to guarantee preemption
was disabled during racing in between wait_on_all_pages_writeback and
f2fs_write_end_io, so that above condition can be avoided.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
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 bf040b5..817cda7 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 (;;) {
+ spin_lock(&sbi->cp_wb_lock);
+
+ while (get_pages(sbi, F2FS_WRITEBACK)) {
prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
- if (!get_pages(sbi, F2FS_WRITEBACK))
- break;
+ spin_unlock(&sbi->cp_wb_lock);
+ io_schedule();
+ spin_lock(&sbi->cp_wb_lock);
- io_schedule_timeout(5*HZ);
+ 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 38ce5d6..8faeada 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 0786a45..cf646b3 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -725,7 +725,8 @@ 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 19a85cf..8b25ac1 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1436,6 +1436,7 @@ 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 */
--
2.7.2
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
2016-04-27 13:41 [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback Chao Yu
@ 2016-04-27 18:09 ` Jaegeuk Kim
2016-04-28 11:51 ` [f2fs-dev] " Chao Yu
0 siblings, 1 reply; 7+ messages in thread
From: Jaegeuk Kim @ 2016-04-27 18:09 UTC (permalink / raw)
To: Chao Yu; +Cc: linux-f2fs-devel, linux-kernel
Hi Chao,
On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
> From: Chao Yu <yuchao0@huawei.com>
>
> The following condition can happen in a preemptible kernel, it may cause
> checkpointer hunging.
>
> 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 can been preempted,
> but there will be no waker since last
> write_end_io has bypassed wake_up. So
> current task will sleep forever.
> - io_schedule_timeout
Well, io_schedule_timeout should work for this?
Thanks,
> Now we use spinlock to create a critical section to guarantee preemption
> was disabled during racing in between wait_on_all_pages_writeback and
> f2fs_write_end_io, so that above condition can be avoided.
>
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
> 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 bf040b5..817cda7 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 (;;) {
> + spin_lock(&sbi->cp_wb_lock);
> +
> + while (get_pages(sbi, F2FS_WRITEBACK)) {
> prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
>
> - if (!get_pages(sbi, F2FS_WRITEBACK))
> - break;
> + spin_unlock(&sbi->cp_wb_lock);
> + io_schedule();
> + spin_lock(&sbi->cp_wb_lock);
>
> - io_schedule_timeout(5*HZ);
> + 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 38ce5d6..8faeada 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 0786a45..cf646b3 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -725,7 +725,8 @@ 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 19a85cf..8b25ac1 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1436,6 +1436,7 @@ 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 */
> --
> 2.7.2
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [f2fs-dev] [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
2016-04-27 18:09 ` Jaegeuk Kim
@ 2016-04-28 11:51 ` Chao Yu
2016-04-28 14:03 ` Peter Zijlstra
0 siblings, 1 reply; 7+ messages in thread
From: Chao Yu @ 2016-04-28 11:51 UTC (permalink / raw)
To: Jaegeuk Kim, peterz; +Cc: Chao Yu, linux-kernel, linux-f2fs-devel
+Cc Peter,
Hi Peter,
This patch should be RFC, I haven't saw such issue in real world though, I still
worry that it may happen. Could you help to have a look at it.
This the question I'd like to ask here is that: in a preemptible kernel, if
thread A add itself into wait queue with TASK_UNINTERRUPTIBLE status through
prepare_to_wait, after that, thread B do the preemption, if there are no waker
for thread A, will thread A sleep forever?
Thanks,
On 2016/4/28 2:09, Jaegeuk Kim wrote:
> Hi Chao,
>
> On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
>> From: Chao Yu <yuchao0@huawei.com>
>>
>> The following condition can happen in a preemptible kernel, it may cause
>> checkpointer hunging.
>>
>> 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 can been preempted,
>> but there will be no waker since last
>> write_end_io has bypassed wake_up. So
>> current task will sleep forever.
>> - io_schedule_timeout
>
> Well, io_schedule_timeout should work for this?
>
> Thanks,
>
>> Now we use spinlock to create a critical section to guarantee preemption
>> was disabled during racing in between wait_on_all_pages_writeback and
>> f2fs_write_end_io, so that above condition can be avoided.
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>> 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 bf040b5..817cda7 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 (;;) {
>> + spin_lock(&sbi->cp_wb_lock);
>> +
>> + while (get_pages(sbi, F2FS_WRITEBACK)) {
>> prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
>>
>> - if (!get_pages(sbi, F2FS_WRITEBACK))
>> - break;
>> + spin_unlock(&sbi->cp_wb_lock);
>> + io_schedule();
>> + spin_lock(&sbi->cp_wb_lock);
>>
>> - io_schedule_timeout(5*HZ);
>> + 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 38ce5d6..8faeada 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 0786a45..cf646b3 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -725,7 +725,8 @@ 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 19a85cf..8b25ac1 100644
>> --- a/fs/f2fs/super.c
>> +++ b/fs/f2fs/super.c
>> @@ -1436,6 +1436,7 @@ 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 */
>> --
>> 2.7.2
>
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>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [f2fs-dev] [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
2016-04-28 11:51 ` [f2fs-dev] " Chao Yu
@ 2016-04-28 14:03 ` Peter Zijlstra
2016-04-28 14:30 ` Chao Yu
0 siblings, 1 reply; 7+ messages in thread
From: Peter Zijlstra @ 2016-04-28 14:03 UTC (permalink / raw)
To: Chao Yu; +Cc: Jaegeuk Kim, Chao Yu, linux-kernel, linux-f2fs-devel
On Thu, Apr 28, 2016 at 07:51:04PM +0800, Chao Yu wrote:
> > On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
> >> From: Chao Yu <yuchao0@huawei.com>
> >>
> >> The following condition can happen in a preemptible kernel, it may cause
> >> checkpointer hunging.
> >>
> >> 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 can been preempted,
> >> but there will be no waker since last
> >> write_end_io has bypassed wake_up. So
> >> current task will sleep forever.
But here, you should be verifying if you really should go sleep; as the
code did; it tests for !get_pages(, F2FS_WRITEBACK), and if you've just
completed that very last one, this will break out.
> >> - io_schedule_timeout
> >
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [f2fs-dev] [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
2016-04-28 14:03 ` Peter Zijlstra
@ 2016-04-28 14:30 ` Chao Yu
2016-04-28 14:37 ` Peter Zijlstra
0 siblings, 1 reply; 7+ messages in thread
From: Chao Yu @ 2016-04-28 14:30 UTC (permalink / raw)
To: Peter Zijlstra, Chao Yu; +Cc: Jaegeuk Kim, linux-kernel, linux-f2fs-devel
On 2016/4/28 22:03, Peter Zijlstra wrote:
> On Thu, Apr 28, 2016 at 07:51:04PM +0800, Chao Yu wrote:
>>> On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
>>>> From: Chao Yu <yuchao0@huawei.com>
>>>>
>>>> The following condition can happen in a preemptible kernel, it may cause
>>>> checkpointer hunging.
>>>>
>>>> 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 can been preempted,
>>>> but there will be no waker since last
>>>> write_end_io has bypassed wake_up. So
>>>> current task will sleep forever.
>
> But here, you should be verifying if you really should go sleep; as the
> code did; it tests for !get_pages(, F2FS_WRITEBACK), and if you've just
> completed that very last one, this will break out.
You mean after being preempted with TASK_UNINTERRUPTIBLE status, that task still
has chance to be scheduled to check '!get_pages(, F2FS_WRITEBACK)', is that right?
>
>>>> - io_schedule_timeout
>>>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [f2fs-dev] [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
2016-04-28 14:30 ` Chao Yu
@ 2016-04-28 14:37 ` Peter Zijlstra
2016-04-28 15:06 ` Chao Yu
0 siblings, 1 reply; 7+ messages in thread
From: Peter Zijlstra @ 2016-04-28 14:37 UTC (permalink / raw)
To: Chao Yu; +Cc: Chao Yu, Jaegeuk Kim, linux-kernel, linux-f2fs-devel
On Thu, Apr 28, 2016 at 10:30:55PM +0800, Chao Yu wrote:
> On 2016/4/28 22:03, Peter Zijlstra wrote:
> > On Thu, Apr 28, 2016 at 07:51:04PM +0800, Chao Yu wrote:
> >>> On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
> >>>> From: Chao Yu <yuchao0@huawei.com>
> >>>>
> >>>> The following condition can happen in a preemptible kernel, it may cause
> >>>> checkpointer hunging.
> >>>>
> >>>> 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 can been preempted,
> >>>> but there will be no waker since last
> >>>> write_end_io has bypassed wake_up. So
> >>>> current task will sleep forever.
> >
> > But here, you should be verifying if you really should go sleep; as the
> > code did; it tests for !get_pages(, F2FS_WRITEBACK), and if you've just
> > completed that very last one, this will break out.
>
> You mean after being preempted with TASK_UNINTERRUPTIBLE status, that task still
> has chance to be scheduled to check '!get_pages(, F2FS_WRITEBACK)', is that right?
Yes, preemption ignores task_struct::state.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [f2fs-dev] [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback
2016-04-28 14:37 ` Peter Zijlstra
@ 2016-04-28 15:06 ` Chao Yu
0 siblings, 0 replies; 7+ messages in thread
From: Chao Yu @ 2016-04-28 15:06 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: Chao Yu, Jaegeuk Kim, linux-kernel, linux-f2fs-devel
On 2016/4/28 22:37, Peter Zijlstra wrote:
> On Thu, Apr 28, 2016 at 10:30:55PM +0800, Chao Yu wrote:
>> On 2016/4/28 22:03, Peter Zijlstra wrote:
>>> On Thu, Apr 28, 2016 at 07:51:04PM +0800, Chao Yu wrote:
>>>>> On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
>>>>>> From: Chao Yu <yuchao0@huawei.com>
>>>>>>
>>>>>> The following condition can happen in a preemptible kernel, it may cause
>>>>>> checkpointer hunging.
>>>>>>
>>>>>> 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 can been preempted,
>>>>>> but there will be no waker since last
>>>>>> write_end_io has bypassed wake_up. So
>>>>>> current task will sleep forever.
>>>
>>> But here, you should be verifying if you really should go sleep; as the
>>> code did; it tests for !get_pages(, F2FS_WRITEBACK), and if you've just
>>> completed that very last one, this will break out.
>>
>> You mean after being preempted with TASK_UNINTERRUPTIBLE status, that task still
>> has chance to be scheduled to check '!get_pages(, F2FS_WRITEBACK)', is that right?
>
> Yes, preemption ignores task_struct::state.
Got it. Thanks very much for your help! :)
>
^ permalink raw reply [flat|nested] 7+ messages in thread
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2016-04-27 13:41 [PATCH RESEND 2/2] f2fs: disable preemption when waiting on all pages writeback Chao Yu
2016-04-27 18:09 ` Jaegeuk Kim
2016-04-28 11:51 ` [f2fs-dev] " Chao Yu
2016-04-28 14:03 ` Peter Zijlstra
2016-04-28 14:30 ` Chao Yu
2016-04-28 14:37 ` Peter Zijlstra
2016-04-28 15:06 ` Chao Yu
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