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Commit 027d6404 authored by Ryusuke Konishi's avatar Ryusuke Konishi
Browse files

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
201913ed.  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: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
parent b5696e5e

fs/nilfs2/mdt.c

+5 −3
Original line number Diff line number Diff line
@@ -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;

}

fs/nilfs2/the_nilfs.c

+1 −2
Original line number Diff line number Diff line
@@ -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);

fs/nilfs2/the_nilfs.h

+6 −21
Original line number Diff line number Diff line
@@ -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)