Hi Chao, On Wed, Apr 27, 2016 at 09:41:48PM +0800, Chao Yu wrote: > From: Chao Yu <[email protected]> > > 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 <[email protected]> > --- > 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 ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
