From 201913ed746c7724a40d33ee5a0b6a1fd2ef3193 Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Date: Tue, 28 Apr 2009 21:04:59 +0900
Subject: [PATCH] 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>
---
fs/nilfs2/ioctl.c | 8 +++++---
fs/nilfs2/mdt.c | 13 +++++++------
2 files changed, 12 insertions(+), 9 deletions(-)
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 108d281ebca5..be387c6b2d46 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -516,14 +516,16 @@ static ssize_t
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;
}
diff --git a/fs/nilfs2/mdt.c b/fs/nilfs2/mdt.c
index 47dd815433fd..e1c6777931b7 100644
--- a/fs/nilfs2/mdt.c
+++ b/fs/nilfs2/mdt.c
@@ -77,19 +77,22 @@ static int nilfs_mdt_create_block(struct inode *inode, unsigned long block,
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 @@ static int nilfs_mdt_create_block(struct inode *inode, unsigned long block,
err = nilfs_transaction_commit(sb);
else
nilfs_transaction_abort(sb);
- if (writer)
- nilfs_put_writer(nilfs);
out:
return err;
}