From 319f63781b05acdf8e771b046c7d4dd77c8d360e Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 25 Dec 2007 16:39:35 -0500 Subject: [PATCH] VFS/fs_stack: use locking around i_size_write in 32-bit systems LTP's iogen01 doio tests hang nicely on 32-bit SMP when /tmp is a unionfs mount of a tmpfs. See the comment on i_size_write in linux/fs.h: it needs to be locked, otherwise i_size_read can spin forever waiting for a lost seqcount update. Most filesystems are already holding i_mutex for this, but unionfs calls fsstack_copy_inode_size from many places, not necessarily holding i_mutex. Use the low-level i_lock within fsstack_copy_inode_size when 32-bit SMP. Checked the entire unionfs code to ensure this is the right fix for i_size_write(). Also compared to what other file systems do when they have to handle inodes, esp. not their own inodes (e.g., network file systems have to access the exported file system's inodes). Found out that most such file systems not just don't lock around i_size_write, but they don't even use i_size_read or i_size_write to access the inode's size. CC: Mike Halcrow Signed-off-by: Hugh Dickins Signed-off-by: Erez Zadok --- fs/stack.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/stack.c b/fs/stack.c index 7913fe53a3c..4336f2b32df 100644 --- a/fs/stack.c +++ b/fs/stack.c @@ -21,8 +21,14 @@ */ void fsstack_copy_inode_size(struct inode *dst, const struct inode *src) { +#if BITS_PER_LONG == 32 && defined(CONFIG_SMP) + spin_lock(&dst->i_lock); +#endif i_size_write(dst, i_size_read(src)); dst->i_blocks = src->i_blocks; +#if BITS_PER_LONG == 32 && defined(CONFIG_SMP) + spin_unlock(&dst->i_lock); +#endif } EXPORT_SYMBOL_GPL(fsstack_copy_inode_size); -- 2.43.0