Messages in this thread Patch in this message | | | Date | Tue, 18 Dec 2007 22:13:25 +0000 (GMT) | From | Hugh Dickins <> | Subject | [PATCH 2/4] unionfs: 32-bit needs lock for i_size |
| |
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.
Signed-off-by: Hugh Dickins <hugh@veritas.com> --- This works for me, to help get through LTP, but is not enough: what about those places which use i_size_write in common code called by unionfs? They ought to participate in this i_locking too. Needs an audit to enumerate such places and decide what course to take.
Bigger question: is unionfs calling down to filesystems without holding their i_mutex, where some may be relying on their i_mutex to be held?
fs/stack.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- 2.6.24-rc5-mm1/fs/stack.c 2007-12-05 10:38:38.000000000 +0000 +++ unionfs2/fs/stack.c 2007-12-05 16:50:15.000000000 +0000 @@ -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((struct inode *)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);
| |