writeback: skip new or to-be-freed inodes

1) I_FREEING tests should be coupled with I_CLEAR

The two I_FREEING tests are racy because clear_inode() can set i_state to
I_CLEAR between the clear of I_SYNC and the test of I_FREEING.

2) skip I_WILL_FREE inodes in generic_sync_sb_inodes() to avoid possible
   races with generic_forget_inode()

generic_forget_inode() sets I_WILL_FREE call writeback on its own, so
generic_sync_sb_inodes() shall not try to step in and create possible races:

  generic_forget_inode
    inode->i_state |= I_WILL_FREE;
    spin_unlock(&inode_lock);
                                       generic_sync_sb_inodes()
                                         spin_lock(&inode_lock);
                                         __iget(inode);
                                         __writeback_single_inode
                                           // see non zero i_count
 may WARN here ==>                         WARN_ON(inode->i_state & I_WILL_FREE);
                                         spin_unlock(&inode_lock);
 may call generic_forget_inode again ==> iput(inode);

The above race and warning didn't turn up because writeback_inodes() holds
the s_umount lock, so generic_forget_inode() finds MS_ACTIVE and returns
early.  But we are not sure the UBIFS calls and future callers will
guarantee that.  So skip I_WILL_FREE inodes for the sake of safety.

Cc: Eric Sandeen <sandeen@sandeen.net>
Acked-by: Jeff Layton <jlayton@redhat.com>
Cc: Masayoshi MIZUMA <m.mizuma@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Acked-by: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 40308e98c6a44f9763354b375ba4c51bb569607a..caf049146ca27a537a7dddc4a38ba02f085a6b35 100644 (file)
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -321,7 +321,7 @@ __sync_single_inode(struct inode *inode, struct writeback_control *wbc)
 
        spin_lock(&inode_lock);
        inode->i_state &= ~I_SYNC;
-       if (!(inode->i_state & I_FREEING)) {
+       if (!(inode->i_state & (I_FREEING | I_CLEAR))) {
                if (!(inode->i_state & I_DIRTY) &&
                    mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
                        /*
@@ -492,7 +492,7 @@ void generic_sync_sb_inodes(struct super_block *sb,
                        break;
                }
 
-               if (inode->i_state & I_NEW) {
+               if (inode->i_state & (I_NEW | I_WILL_FREE)) {
                        requeue_io(inode);
                        continue;
                }
@@ -523,7 +523,7 @@ void generic_sync_sb_inodes(struct super_block *sb,
                if (current_is_pdflush() && !writeback_acquire(bdi))
                        break;
 
-               BUG_ON(inode->i_state & I_FREEING);
+               BUG_ON(inode->i_state & (I_FREEING | I_CLEAR));
                __iget(inode);
                pages_skipped = wbc->pages_skipped;
                __writeback_single_inode(inode, wbc);