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
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
