f2fs: fix a deadlock in fsync

This patch fixes a deadlock bug that occurs quite often when there are
concurrent write and fsync on a same file.

Following is the simplified call trace when tasks get hung.

fsync thread:
- f2fs_sync_file
 ...
 - f2fs_write_data_pages
 ...
  - update_extent_cache
  ...
   - update_inode
    - wait_on_page_writeback

bdi writeback thread
- __writeback_single_inode
 - f2fs_write_data_pages
  - mutex_lock(sbi->writepages)

The deadlock happens when the fsync thread waits on a inode page that has
been added to the f2fs' cached bio sbi->bio[NODE], and unfortunately,
no one else could be able to submit the cached bio to block layer for
writeback. This is because the fsync thread already hold a sbi->fs_lock and
the sbi->writepages lock, causing the bdi thread being blocked when attempt
to write data pages for the same inode. At the same time, f2fs_gc thread
does not notice the situation and could not help. Even the sync syscall
gets blocked.

To fix it, we could submit the cached bio first before waiting on a inode page
that is being written back.

Signed-off-by: Jin Xu <jinuxstyle@gmail.com>
[Jaegeuk Kim: add more cases to use f2fs_wait_on_page_writeback]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

5 files changed, 16 insertions, 9 deletions

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index f458883af815..a7eb52925723 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -37,7 +37,7 @@ static void __set_data_blkaddr(struct dnode_of_data *dn, block_t new_addr)
         struct page *node_page = dn->node_page;
         unsigned int ofs_in_node = dn->ofs_in_node;
 
-        wait_on_page_writeback(node_page);
+        f2fs_wait_on_page_writeback(node_page, NODE, false);
 
         rn = F2FS_NODE(node_page);
 
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 63813befdd82..13db10b70e66 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1023,7 +1023,8 @@ int npages_for_summary_flush(struct f2fs_sb_info *);
 void allocate_new_segments(struct f2fs_sb_info *);
 struct page *get_sum_page(struct f2fs_sb_info *, unsigned int);
 struct bio *f2fs_bio_alloc(struct block_device *, int);
-void f2fs_submit_bio(struct f2fs_sb_info *, enum page_type, bool sync);
+void f2fs_submit_bio(struct f2fs_sb_info *, enum page_type, bool);
+void f2fs_wait_on_page_writeback(struct page *, enum page_type, bool);
 void write_meta_page(struct f2fs_sb_info *, struct page *);
 void write_node_page(struct f2fs_sb_info *, struct page *, unsigned int,
                                         block_t, block_t *);
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index d286d8be8e68..e6b3ffd5ff6a 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -422,8 +422,7 @@ next_step:
 
                 /* set page dirty and write it */
                 if (gc_type == FG_GC) {
-                        f2fs_submit_bio(sbi, NODE, true);
-                        wait_on_page_writeback(node_page);
+                        f2fs_wait_on_page_writeback(node_page, NODE, true);
                         set_page_dirty(node_page);
                 } else {
                         if (!PageWriteback(node_page))
@@ -523,10 +522,7 @@ static void move_data_page(struct inode *inode, struct page *page, int gc_type)
         } else {
                 struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
 
-                if (PageWriteback(page)) {
-                        f2fs_submit_bio(sbi, DATA, true);
-                        wait_on_page_writeback(page);
-                }
+                f2fs_wait_on_page_writeback(page, DATA, true);
 
                 if (clear_page_dirty_for_io(page) &&
                         S_ISDIR(inode->i_mode)) {
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index debf74308045..9ab81e7472c5 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -151,7 +151,7 @@ void update_inode(struct inode *inode, struct page *node_page)
         struct f2fs_node *rn;
         struct f2fs_inode *ri;
 
-        wait_on_page_writeback(node_page);
+        f2fs_wait_on_page_writeback(node_page, NODE, false);
 
         rn = F2FS_NODE(node_page);
         ri = &(rn->i);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 9b74ae2137d1..68e344f9e042 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -705,6 +705,16 @@ retry:
         trace_f2fs_submit_write_page(page, blk_addr, type);
 }
 
+void f2fs_wait_on_page_writeback(struct page *page,
+                                enum page_type type, bool sync)
+{
+        struct f2fs_sb_info *sbi = F2FS_SB(page->mapping->host->i_sb);
+        if (PageWriteback(page)) {
+                f2fs_submit_bio(sbi, type, sync);
+                wait_on_page_writeback(page);
+        }
+}
+
 static bool __has_curseg_space(struct f2fs_sb_info *sbi, int type)
 {
         struct curseg_info *curseg = CURSEG_I(sbi, type);