Re: [PATCH] f2fs: use f2fs_iget_nowait again

[Jaegeuk Kim]

change log from v1:
 o found another deadlock case, so change the approach

From 145b6ee0b2523bad0e28c09f4ac5bb050cd22085 Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaegeuk.kim@xxxxxxxxxxx>
Date: Tue, 30 Apr 2013 11:33:27 +0900
Subject: [PATCH] f2fs: avoid deadlock during evict after f2fs_gc
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx,
linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx

o Deadlock case #1

Thread 1:
- writeback_sb_inodes
 - do_writepages
  - f2fs_write_data_pages
   - write_cache_pages
    - f2fs_write_data_page
     - f2fs_balance_fs
      - wait mutex_lock(gc_mutex)

Thread 2:
- f2fs_balance_fs
 - mutex_lock(gc_mutex)
 - f2fs_gc
  - f2fs_iget
   - wait iget_locked(inode->i_lock)

Thread 3:
- do_unlinkat
 - iput
  - lock(inode->i_lock)
   - evict
    - inode_wait_for_writeback

o Deadlock case #2

Thread 1:
- __writeback_single_inode
 : set I_SYNC
  - do_writepages
   - f2fs_write_data_page
    - f2fs_balance_fs
     - f2fs_gc
      - iput
       - evict
        - inode_wait_for_writeback(I_SYNC)

In order to avoid this, even though iput is called with the
zero-reference
count, we need to stop the eviction procedure if the inode is on
writeback.
So this patch links f2fs_drop_inode which checks the I_SYNC flag.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@xxxxxxxxxxx>
---
 fs/f2fs/super.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index b015b6c..e1c54e4 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -99,6 +99,13 @@ static struct inode *f2fs_alloc_inode(struct
super_block *sb)
 	return &fi->vfs_inode;
 }
 
+static int f2fs_drop_inode(struct inode *inode)
+{
+	if (inode->i_state & I_SYNC)
+		return 0;
+	return generic_drop_inode(inode);
+}
+
 static void f2fs_i_callback(struct rcu_head *head)
 {
 	struct inode *inode = container_of(head, struct inode, i_rcu);
@@ -233,6 +240,7 @@ static int f2fs_show_options(struct seq_file *seq,
struct dentry *root)
 
 static struct super_operations f2fs_sops = {
 	.alloc_inode	= f2fs_alloc_inode,
+	.drop_inode	= f2fs_drop_inode,
 	.destroy_inode	= f2fs_destroy_inode,
 	.write_inode	= f2fs_write_inode,
 	.show_options	= f2fs_show_options,
-- 
1.8.1.3.566.gaa39828



-- 
Jaegeuk Kim
Samsung

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