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On Mon, Oct 19, 2009 at 12:05:26AM -0400, Christoph Hellwig wrote:
> The iolock is used for protecting reads, writes and block truncates against
> each other. We have two classes of callers, the first one is induced by
> a file operation and requires a reference to the inode be held and not
> dropped after the operation is done:
>
> - xfs_vm_vmap, xfs_vn_fallocate, xfs_read, xfs_write, xfs_splice_read,
> xfs_splice_write and xfs_setattr are all implementations of VFS methods
> that require a live inode
> - xfs_getbmap and xfs_swap_extents are ioctl subcommand for which the
> same is true
> - xfs_truncate_file is only called on quota inodes just returned from
> xfs_iget
> - xfs_sync_inode_data does the lock just after an igrab()
> - xfs_filestream_associate and xfs_filestream_new_ag take the iolock on the
> parent inode of an inode which by VFS rules must be referenced
>
> And we have various calls to truncate blocks past EOF or the whole file when
> dropping the last reference to an inode. Unfortunately lockdep complains
> when we do memory allocations that can recurse into the filesystem in the
> first class because the second class happens to take the same lock. To avoid
> this re-init the iolock in the beginning of xfs_fs_clear_inode to get
> a new lock class.
>
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
>
> Index: xfs/fs/xfs/linux-2.6/xfs_super.c
> ===================================================================
> --- xfs.orig/fs/xfs/linux-2.6/xfs_super.c 2009-10-14 17:24:31.356278624
> +0200
> +++ xfs/fs/xfs/linux-2.6/xfs_super.c 2009-10-19 06:03:05.771006625 +0200
> @@ -999,7 +999,6 @@ xfs_fs_inode_init_once(
>
> mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
> "xfsino", ip->i_ino);
> - mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
> }
>
> /*
> @@ -1101,6 +1100,22 @@ xfs_fs_clear_inode(
> XFS_STATS_INC(vn_remove);
> XFS_STATS_DEC(vn_active);
>
> + /*
> + * The iolock is used for protecting reads, writes and block truncates
> + * against each other. We have two classes of callers, the first one
> + * is induced by a file operation and requires a reference to the
> + * inode be held and not dropped after the operation is done, and
> + * second we have various calls to truncate blocks past EOF or for the
> + * whole file when dropping the last reference to an inode.
> + * Unfortunately lockdep complains when we do memory allocations that
> + * can recurse into the filesystem in the first class because the
> + * second class happens to take the same lock. To avoid this
> + * reinitialize the iolock in the beginning of xfs_fs_clear_inode to
> + * get a new lock class.
> + */
> + ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
> + mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
> +
> xfs_inactive(ip);
> }
>
> Index: xfs/fs/xfs/xfs_iget.c
> ===================================================================
> --- xfs.orig/fs/xfs/xfs_iget.c 2009-10-14 17:25:26.733004131 +0200
> +++ xfs/fs/xfs/xfs_iget.c 2009-10-14 17:28:26.272274357 +0200
> @@ -73,6 +73,9 @@ xfs_inode_alloc(
> ASSERT(atomic_read(&ip->i_pincount) == 0);
> ASSERT(!spin_is_locked(&ip->i_flags_lock));
> ASSERT(completion_done(&ip->i_flush));
> + ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
> +
> + mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);
>
> /* initialise the xfs inode */
> ip->i_ino = ino;
>
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