Re: [PATCH v3] f2fs: use f2fs_iget_nowait again

[Jaegeuk Kim]

change log from v2:
  o slighly change the previous approach

From 42e49df33bacafc20434e39fc127c9722c9f8691 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/f2fs.h  |  1 +
 fs/f2fs/gc.c    |  1 +
 fs/f2fs/super.c | 19 +++++++++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 20aab02..beb3f06 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -846,6 +846,7 @@ enum {
 	FI_INC_LINK,		/* need to increment i_nlink */
 	FI_ACL_MODE,		/* indicate acl mode */
 	FI_NO_ALLOC,		/* should not allocate any blocks */
+	FI_ON_GC,		/* indicate inode is on gc */
 };
 
 static inline void set_inode_flag(struct f2fs_inode_info *fi, int flag)
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 1496159..258b786 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -345,6 +345,7 @@ repeat:
 	}
 	new_ie->inode = inode;
 	list_add_tail(&new_ie->list, ilist);
+	set_inode_flag(F2FS_I(inode), FI_ON_GC);
 }
 
 static void put_gc_inode(struct list_head *ilist)
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 5835aaf..6ac1f42 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -98,6 +98,24 @@ static struct inode *f2fs_alloc_inode(struct
super_block *sb)
 	return &fi->vfs_inode;
 }
 
+static int f2fs_drop_inode(struct inode *inode)
+{
+	int drop = generic_drop_inode(inode);
+
+	/*
+	 * This is to avoid a deadlock condition like below.
+	 * writeback_single_inode(inode)
+	 *  - f2fs_write_data_page
+	 *    - f2fs_gc -> iput -> evict
+	 *       - inode_wait_for_writeback(inode)
+	 */
+	if (inode->i_state & I_SYNC &&
+			is_inode_flag_set(F2FS_I(inode), FI_ON_GC))
+		drop = 0;
+	clear_inode_flag(F2FS_I(inode), FI_ON_GC);
+	return drop;
+}
+
 static void f2fs_i_callback(struct rcu_head *head)
 {
 	struct inode *inode = container_of(head, struct inode, i_rcu);
@@ -232,6 +250,7 @@ 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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