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authorJan Kara <jack@suse.cz>2012-05-03 16:48:03 +0400
committerFengguang Wu <fengguang.wu@intel.com>2012-05-06 09:43:41 +0400
commit169ebd90131b2ffca74bb2dbe7eeacd39fb83714 (patch)
tree513136e110970da388680947c225ef8ca05a6dd7 /include/linux/fs.h
parentdbd5768f87ff6fb0a4fe09c4d7b6c4a24de99430 (diff)
downloadlinux-169ebd90131b2ffca74bb2dbe7eeacd39fb83714.tar.xz
writeback: Avoid iput() from flusher thread
Doing iput() from flusher thread (writeback_sb_inodes()) can create problems because iput() can do a lot of work - for example truncate the inode if it's the last iput on unlinked file. Some filesystems depend on flusher thread progressing (e.g. because they need to flush delay allocated blocks to reduce allocation uncertainty) and so flusher thread doing truncate creates interesting dependencies and possibilities for deadlocks. We get rid of iput() in flusher thread by using the fact that I_SYNC inode flag effectively pins the inode in memory. So if we take care to either hold i_lock or have I_SYNC set, we can get away without taking inode reference in writeback_sb_inodes(). As a side effect of these changes, we also fix possible use-after-free in wb_writeback() because inode_wait_for_writeback() call could try to reacquire i_lock on the inode that was already free. Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Diffstat (limited to 'include/linux/fs.h')
-rw-r--r--include/linux/fs.h7
1 files changed, 4 insertions, 3 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c79316c79ee3..1c71e7f4d234 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1753,9 +1753,10 @@ struct super_operations {
* anew. Other functions will just ignore such inodes,
* if appropriate. I_NEW is used for waiting.
*
- * I_SYNC Synchonized write of dirty inode data. The bits is
- * set during data writeback, and cleared with a wakeup
- * on the bit address once it is done.
+ * I_SYNC Writeback of inode is running. The bit is set during
+ * data writeback, and cleared with a wakeup on the bit
+ * address once it is done. The bit is also used to pin
+ * the inode in memory for flusher thread.
*
* I_REFERENCED Marks the inode as recently references on the LRU list.
*