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Commit 201913ed authored by Ryusuke Konishi's avatar Ryusuke Konishi
Browse files

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: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
parent 85c2a74f

fs/nilfs2/ioctl.c

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

}

fs/nilfs2/mdt.c

+7 −6
Original line number Diff line number Diff line
@@ -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;

}