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Commit 26931309 authored by Frederic Weisbecker's avatar Frederic Weisbecker
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kill-the-bkl/reiserfs: lock only once on reiserfs_get_block() 



reiserfs_get_block() is one of these sites where the write lock might
be acquired recursively.

It's a particular problem because this function is called very often.
It's a hot spot which needs to reschedule() periodically while converting
direct items to indirect ones because it can take some time.

Then if we are applying the write lock release/reacquire pattern on
schedule() here, it may not produce the desired effect since we may have
locked in more than one depth.

The solution is to use reiserfs_write_lock_once() which won't try
to reacquire the lock recursively. Then the lock will be *really*
released before schedule().

Also, we only release the lock if TIF_NEED_RESCHED is set to not
create wasteful numerous contentions.

[ Impact: fix a too long holded lock case in reiserfs_get_block() ]

Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent d663af80

fs/reiserfs/inode.c

+11 −8
Original line number Diff line number Diff line
@@ -605,6 +605,7 @@ int reiserfs_get_block(struct inode *inode, sector_t block, 
	__le32 *item;

	int done;

	int fs_gen;

	int lock_depth;

	struct reiserfs_transaction_handle *th = NULL;

	/* space reserved in transaction batch:

	   . 3 balancings in direct->indirect conversion
@@ -620,11 +621,11 @@ int reiserfs_get_block(struct inode *inode, sector_t block, 
	loff_t new_offset =

	    (((loff_t) block) << inode->i_sb->s_blocksize_bits) + 1;



	reiserfs_write_lock(inode->i_sb);

	lock_depth = reiserfs_write_lock_once(inode->i_sb);

	version = get_inode_item_key_version(inode);



	if (!file_capable(inode, block)) {

		reiserfs_write_unlock(inode->i_sb);

		reiserfs_write_unlock_once(inode->i_sb, lock_depth);

		return -EFBIG;

	}
@@ -636,7 +637,7 @@ int reiserfs_get_block(struct inode *inode, sector_t block, 
		/* find number of block-th logical block of the file */

		ret = _get_block_create_0(inode, block, bh_result,

					  create | GET_BLOCK_READ_DIRECT);

		reiserfs_write_unlock(inode->i_sb);

		reiserfs_write_unlock_once(inode->i_sb, lock_depth);

		return ret;

	}

	/*
@@ -754,7 +755,7 @@ int reiserfs_get_block(struct inode *inode, sector_t block, 
		if (!dangle && th)

			retval = reiserfs_end_persistent_transaction(th);



		reiserfs_write_unlock(inode->i_sb);

		reiserfs_write_unlock_once(inode->i_sb, lock_depth);



		/* the item was found, so new blocks were not added to the file

		 ** there is no need to make sure the inode is updated with this
@@ -1005,9 +1006,11 @@ int reiserfs_get_block(struct inode *inode, sector_t block, 
		 * long time.  reschedule if needed and also release the write

		 * lock for others.

		 */

		reiserfs_write_unlock(inode->i_sb);

		cond_resched();

		reiserfs_write_lock(inode->i_sb);

		if (need_resched()) {

			reiserfs_write_unlock_once(inode->i_sb, lock_depth);

			schedule();

			lock_depth = reiserfs_write_lock_once(inode->i_sb);

		}



		retval = search_for_position_by_key(inode->i_sb, &key, &path);

		if (retval == IO_ERROR) {
@@ -1042,7 +1045,7 @@ int reiserfs_get_block(struct inode *inode, sector_t block, 
			retval = err;

	}



	reiserfs_write_unlock(inode->i_sb);

	reiserfs_write_unlock_once(inode->i_sb, lock_depth);

	reiserfs_check_path(&path);

	return retval;

}