Hi Chao,
On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote:
> From: Chao Yu <yuch...@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 <yuch...@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
