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Re: [PATCH] xfs: reset the i_iolock lock class in the reclaim path

To: xfs@xxxxxxxxxxx
Subject: Re: [PATCH] xfs: reset the i_iolock lock class in the reclaim path
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Fri, 30 Oct 2009 04:55:33 -0400
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
In-reply-to: <20091019040526.GC21115@xxxxxxxxxxxxx>
References: <20091019040526.GC21115@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.19 (2009-01-05)
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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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---end quoted text---

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