nilfs2: fix circular locking dependency of writer mutex
This fixes the following circular locking dependency problem:
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.30-rc3 #5
-------------------------------------------------------
segctord/3895 is trying to acquire lock:
(&nilfs->ns_writer_mutex){+.+...}, at: [<d0d02172>]
nilfs_mdt_get_block+0x89/0x20f [nilfs2]
but task is already holding lock:
(&bmap->b_sem){++++..}, at: [<d0d02d99>]
nilfs_bmap_propagate+0x14/0x2e [nilfs2]
which lock already depends on the new lock.
The bugfix is done by replacing call sites of nilfs_get_writer() which
are never called from read-only context with direct dereferencing of
pointer to a writable FS-instance.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/mdt.c b/fs/nilfs2/mdt.c
index 47dd815..e1c6777 100644
--- a/fs/nilfs2/mdt.c
+++ b/fs/nilfs2/mdt.c
@@ -77,19 +77,22 @@
void *))
{
struct the_nilfs *nilfs = NILFS_MDT(inode)->mi_nilfs;
- struct nilfs_sb_info *writer = NULL;
struct super_block *sb = inode->i_sb;
struct nilfs_transaction_info ti;
struct buffer_head *bh;
int err;
if (!sb) {
- writer = nilfs_get_writer(nilfs);
- if (!writer) {
+ /*
+ * Make sure this function is not called from any
+ * read-only context.
+ */
+ if (!nilfs->ns_writer) {
+ WARN_ON(1);
err = -EROFS;
goto out;
}
- sb = writer->s_super;
+ sb = nilfs->ns_writer->s_super;
}
nilfs_transaction_begin(sb, &ti, 0);
@@ -127,8 +130,6 @@
err = nilfs_transaction_commit(sb);
else
nilfs_transaction_abort(sb);
- if (writer)
- nilfs_put_writer(nilfs);
out:
return err;
}