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authorRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>2009-08-02 22:45:33 +0900
committerRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>2009-09-14 18:27:13 +0900
commit027d6404eb4327878454db72a006adfcb8001bb8 (patch)
tree671c0d84ee5fd19ef85a3ff15d99a3519c1ed8bf /fs
parentb5696e5e0dbfb6323277d51d67d230317c18aba9 (diff)
downloadlinux-027d6404eb4327878454db72a006adfcb8001bb8.tar.gz
nilfs2: use semaphore to protect pointer to a writable FS-instance
will get rid of nilfs_get_writer() and nilfs_put_writer() pair used to retain a writable FS-instance for a period. The pair functions were making up some kind of recursive lock with a mutex, but they became overkill since the commit 201913ed746c7724a40d33ee5a0b6a1fd2ef3193. Furthermore, they caused the following lockdep warning because the mutex can be released by a task which didn't lock it: ===================================== [ BUG: bad unlock balance detected! ] ------------------------------------- kswapd0/422 is trying to release lock (&nilfs->ns_writer_mutex) at: [<c1359ff5>] mutex_unlock+0x8/0xa but there are no more locks to release! other info that might help us debug this: no locks held by kswapd0/422. stack backtrace: Pid: 422, comm: kswapd0 Not tainted 2.6.31-rc4-nilfs #51 Call Trace: [<c1358f97>] ? printk+0xf/0x18 [<c104fea7>] print_unlock_inbalance_bug+0xcc/0xd7 [<c11578de>] ? prop_put_global+0x3/0x35 [<c1050195>] lock_release+0xed/0x1dc [<c1359ff5>] ? mutex_unlock+0x8/0xa [<c1359f83>] __mutex_unlock_slowpath+0xaf/0x119 [<c1359ff5>] mutex_unlock+0x8/0xa [<d1284add>] nilfs_mdt_write_page+0xd8/0xe1 [nilfs2] [<c1092653>] shrink_page_list+0x379/0x68d [<c109171b>] ? isolate_pages_global+0xb4/0x18c [<c1092bd2>] shrink_list+0x26b/0x54b [<c10930be>] shrink_zone+0x20c/0x2a2 [<c10936b7>] kswapd+0x407/0x591 [<c1091667>] ? isolate_pages_global+0x0/0x18c [<c1040603>] ? autoremove_wake_function+0x0/0x33 [<c10932b0>] ? kswapd+0x0/0x591 [<c104033b>] kthread+0x69/0x6e [<c10402d2>] ? kthread+0x0/0x6e [<c1003e33>] kernel_thread_helper+0x7/0x1a This patch uses a reader/writer semaphore instead of the own lock and kills this warning. Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Diffstat (limited to 'fs')
-rw-r--r--fs/nilfs2/mdt.c8
-rw-r--r--fs/nilfs2/the_nilfs.c3
-rw-r--r--fs/nilfs2/the_nilfs.h27
3 files changed, 12 insertions, 26 deletions
diff --git a/fs/nilfs2/mdt.c b/fs/nilfs2/mdt.c
index 2dfd47714ae..a5cd80162dc 100644
--- a/fs/nilfs2/mdt.c
+++ b/fs/nilfs2/mdt.c
@@ -402,6 +402,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
struct inode *inode = container_of(page->mapping,
struct inode, i_data);
struct super_block *sb = inode->i_sb;
+ struct the_nilfs *nilfs = NILFS_MDT(inode)->mi_nilfs;
struct nilfs_sb_info *writer = NULL;
int err = 0;
@@ -411,9 +412,10 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
if (page->mapping->assoc_mapping)
return 0; /* Do not request flush for shadow page cache */
if (!sb) {
- writer = nilfs_get_writer(NILFS_MDT(inode)->mi_nilfs);
+ down_read(&nilfs->ns_writer_sem);
+ writer = nilfs->ns_writer;
if (!writer) {
- nilfs_put_writer(NILFS_MDT(inode)->mi_nilfs);
+ up_read(&nilfs->ns_writer_sem);
return -EROFS;
}
sb = writer->s_super;
@@ -425,7 +427,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
nilfs_flush_segment(sb, inode->i_ino);
if (writer)
- nilfs_put_writer(NILFS_MDT(inode)->mi_nilfs);
+ up_read(&nilfs->ns_writer_sem);
return err;
}
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 8b888982571..0c4573653b8 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -68,12 +68,11 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
nilfs->ns_bdev = bdev;
atomic_set(&nilfs->ns_count, 1);
- atomic_set(&nilfs->ns_writer_refcount, -1);
atomic_set(&nilfs->ns_ndirtyblks, 0);
init_rwsem(&nilfs->ns_sem);
init_rwsem(&nilfs->ns_super_sem);
mutex_init(&nilfs->ns_mount_mutex);
- mutex_init(&nilfs->ns_writer_mutex);
+ init_rwsem(&nilfs->ns_writer_sem);
INIT_LIST_HEAD(&nilfs->ns_list);
INIT_LIST_HEAD(&nilfs->ns_supers);
spin_lock_init(&nilfs->ns_last_segment_lock);
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index 1b9caafb866..fa3a1dfe405 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -50,8 +50,7 @@ enum {
* @ns_sem: semaphore for shared states
* @ns_super_sem: semaphore for global operations across super block instances
* @ns_mount_mutex: mutex protecting mount process of nilfs
- * @ns_writer_mutex: mutex protecting ns_writer attach/detach
- * @ns_writer_refcount: number of referrers on ns_writer
+ * @ns_writer_sem: semaphore protecting ns_writer attach/detach
* @ns_current: back pointer to current mount
* @ns_sbh: buffer heads of on-disk super blocks
* @ns_sbp: pointers to super block data
@@ -100,8 +99,7 @@ struct the_nilfs {
struct rw_semaphore ns_sem;
struct rw_semaphore ns_super_sem;
struct mutex ns_mount_mutex;
- struct mutex ns_writer_mutex;
- atomic_t ns_writer_refcount;
+ struct rw_semaphore ns_writer_sem;
/*
* components protected by ns_super_sem
@@ -221,34 +219,21 @@ static inline void get_nilfs(struct the_nilfs *nilfs)
atomic_inc(&nilfs->ns_count);
}
-static inline struct nilfs_sb_info *nilfs_get_writer(struct the_nilfs *nilfs)
-{
- if (atomic_inc_and_test(&nilfs->ns_writer_refcount))
- mutex_lock(&nilfs->ns_writer_mutex);
- return nilfs->ns_writer;
-}
-
-static inline void nilfs_put_writer(struct the_nilfs *nilfs)
-{
- if (atomic_add_negative(-1, &nilfs->ns_writer_refcount))
- mutex_unlock(&nilfs->ns_writer_mutex);
-}
-
static inline void
nilfs_attach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
{
- mutex_lock(&nilfs->ns_writer_mutex);
+ down_write(&nilfs->ns_writer_sem);
nilfs->ns_writer = sbi;
- mutex_unlock(&nilfs->ns_writer_mutex);
+ up_write(&nilfs->ns_writer_sem);
}
static inline void
nilfs_detach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
{
- mutex_lock(&nilfs->ns_writer_mutex);
+ down_write(&nilfs->ns_writer_sem);
if (sbi == nilfs->ns_writer)
nilfs->ns_writer = NULL;
- mutex_unlock(&nilfs->ns_writer_mutex);
+ up_write(&nilfs->ns_writer_sem);
}
static inline void nilfs_put_sbinfo(struct nilfs_sb_info *sbi)