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/ioctl.c b/fs/nilfs2/ioctl.c
index 108d281..be387c6 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -516,14 +516,16 @@
nilfs_ioctl_do_free_segments(struct the_nilfs *nilfs, __u64 *posp, int flags,
void *buf, size_t size, size_t nmembs)
{
- struct nilfs_sb_info *sbi = nilfs_get_writer(nilfs);
+ struct nilfs_sb_info *sbi = nilfs->ns_writer;
int ret;
- if (unlikely(!sbi))
+ if (unlikely(!sbi)) {
+ /* never happens because called for a writable mount */
+ WARN_ON(1);
return -EROFS;
+ }
ret = nilfs_segctor_add_segments_to_be_freed(
NILFS_SC(sbi), buf, nmembs);
- nilfs_put_writer(nilfs);
return (ret < 0) ? ret : nmembs;
}