logfs: take write mutex lock during fsync and sync

LogFS uses super->s_write_mutex while writing data to disk. Taking the
same mutex lock in sync and fsync code path solves the following BUG:

------------[ cut here ]------------
kernel BUG at /home/prasad/logfs/dev_bdev.c:134!

Pid: 2387, comm: flush-253:16 Not tainted 3.0.0+ #4 Bochs Bochs
RIP: 0010:[<ffffffffa007deed>]  [<ffffffffa007deed>]
                bdev_writeseg+0x25d/0x270 [logfs]
Call Trace:
[<ffffffffa007c381>] logfs_open_area+0x91/0x150 [logfs]
[<ffffffff8128dcb2>] ? find_level.clone.9+0x62/0x100
[<ffffffffa007c49c>] __logfs_segment_write.clone.20+0x5c/0x190 [logfs]
[<ffffffff810ef005>] ? mempool_kmalloc+0x15/0x20
[<ffffffff810ef383>] ? mempool_alloc+0x53/0x130
[<ffffffffa007c7a4>] logfs_segment_write+0x1d4/0x230 [logfs]
[<ffffffffa0078f8e>] logfs_write_i0+0x12e/0x190 [logfs]
[<ffffffffa0079300>] __logfs_write_rec+0x140/0x220 [logfs]
[<ffffffffa0079444>] logfs_write_rec+0x64/0xd0 [logfs]
[<ffffffffa00795b6>] __logfs_write_buf+0x106/0x110 [logfs]
[<ffffffffa007a13e>] logfs_write_buf+0x4e/0x80 [logfs]
[<ffffffffa0073e33>] __logfs_writepage+0x23/0x80 [logfs]
[<ffffffffa007410c>] logfs_writepage+0xdc/0x110 [logfs]
[<ffffffff810f5ba7>] __writepage+0x17/0x40
[<ffffffff810f6208>] write_cache_pages+0x208/0x4f0
[<ffffffff810f5b90>] ? set_page_dirty+0x70/0x70
[<ffffffff810f653a>] generic_writepages+0x4a/0x70
[<ffffffff810f75d1>] do_writepages+0x21/0x40
[<ffffffff8116b9d1>] writeback_single_inode+0x101/0x250
[<ffffffff8116bdbd>] writeback_sb_inodes+0xed/0x1c0
[<ffffffff8116c5fb>] writeback_inodes_wb+0x7b/0x1e0
[<ffffffff8116cc23>] wb_writeback+0x4c3/0x530
[<ffffffff814d984d>] ? sub_preempt_count+0x9d/0xd0
[<ffffffff8116cd6b>] wb_do_writeback+0xdb/0x290
[<ffffffff814d984d>] ? sub_preempt_count+0x9d/0xd0
[<ffffffff814d6208>] ? _raw_spin_unlock_irqrestore+0x18/0x40
[<ffffffff8105aa5a>] ? del_timer+0x8a/0x120
[<ffffffff8116cfac>] bdi_writeback_thread+0x8c/0x2e0
[<ffffffff8116cf20>] ? wb_do_writeback+0x290/0x290
[<ffffffff8106d2e6>] kthread+0x96/0xa0
[<ffffffff814de514>] kernel_thread_helper+0x4/0x10
[<ffffffff8106d250>] ? kthread_worker_fn+0x190/0x190
[<ffffffff814de510>] ? gs_change+0xb/0xb
RIP  [<ffffffffa007deed>] bdev_writeseg+0x25d/0x270 [logfs]
---[ end trace 0211ad60a57657c4 ]---

Reviewed-by: Joern Engel <joern@logfs.org>
Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>

fs/logfs/file.c

@@ -230,7 +230,9 @@ int logfs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 		return ret;
 
 	mutex_lock(&inode->i_mutex);
+	logfs_get_wblocks(sb, NULL, WF_LOCK);
 	logfs_write_anchor(sb);
+	logfs_put_wblocks(sb, NULL, WF_LOCK);
 	mutex_unlock(&inode->i_mutex);
 
 	return 0;

fs/logfs/inode.c

@@ -364,7 +364,9 @@ static void logfs_init_once(void *_li)
 
 static int logfs_sync_fs(struct super_block *sb, int wait)
 {
+	logfs_get_wblocks(sb, NULL, WF_LOCK);
 	logfs_write_anchor(sb);
+	logfs_put_wblocks(sb, NULL, WF_LOCK);
 	return 0;
 }
 

fs/logfs/logfs.h

@@ -577,6 +577,8 @@ void initialize_block_counters(struct page *page, struct logfs_block *block,
 		__be64 *array, int page_is_empty);
 int logfs_exist_block(struct inode *inode, u64 bix);
 int get_page_reserve(struct inode *inode, struct page *page);
+void logfs_get_wblocks(struct super_block *sb, struct page *page, int lock);
+void logfs_put_wblocks(struct super_block *sb, struct page *page, int lock);
 extern struct logfs_block_ops indirect_block_ops;
 
 /* segment.c */

fs/logfs/readwrite.c

@@ -244,8 +244,7 @@ static void preunlock_page(struct super_block *sb, struct page *page, int lock)
  * is waiting for s_write_mutex.  We annotate this fact by setting PG_pre_locked
  * in addition to PG_locked.
  */
-static void logfs_get_wblocks(struct super_block *sb, struct page *page,
-		int lock)
+void logfs_get_wblocks(struct super_block *sb, struct page *page, int lock)
 {
 	struct logfs_super *super = logfs_super(sb);
 
@@ -260,8 +259,7 @@ static void logfs_get_wblocks(struct super_block *sb, struct page *page,
 	}
 }
 
-static void logfs_put_wblocks(struct super_block *sb, struct page *page,
-		int lock)
+void logfs_put_wblocks(struct super_block *sb, struct page *page, int lock)
 {
 	struct logfs_super *super = logfs_super(sb);