Patchwork [1/8] far: remove i_alloc_sem abuse

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Submitter Christoph Hellwig
Date June 20, 2011, 8:15 p.m.
Message ID <20110620202030.577464178@bombadil.infradead.org>
Download mbox | patch
Permalink /patch/101195/
State Superseded
Headers show

Comments

Christoph Hellwig - June 20, 2011, 8:15 p.m.
Add a new rw_semaphore to protect bmap against truncate.  Previous
i_alloc_sem was abused for this, but it's going away in this series.

Signed-off-by: Christoph Hellwig <hch@lst.de>


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OGAWA Hirofumi - June 21, 2011, 3:57 p.m.
Christoph Hellwig <hch@infradead.org> writes:

> Add a new rw_semaphore to protect bmap against truncate.  Previous
> i_alloc_sem was abused for this, but it's going away in this series.

In FAT case, ->i_mutex was better. But, last time I saw, shmfs was using
->i_mutex to call ->bmap. So, this was chosen instead.

I'm not checking current version yet though, if shmfs had change, we can
use ->i_mutex.

BTW, this patch looks good to me.

Thanks.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
>
> Index: linux-2.6/fs/fat/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/fat/inode.c	2011-06-20 21:28:19.707963855 +0200
> +++ linux-2.6/fs/fat/inode.c	2011-06-20 21:29:25.031293882 +0200
> @@ -224,9 +224,9 @@ static sector_t _fat_bmap(struct address
>  	sector_t blocknr;
>  
>  	/* fat_get_cluster() assumes the requested blocknr isn't truncated. */
> -	down_read(&mapping->host->i_alloc_sem);
> +	down_read(&MSDOS_I(mapping->host)->truncate_lock);
>  	blocknr = generic_block_bmap(mapping, block, fat_get_block);
> -	up_read(&mapping->host->i_alloc_sem);
> +	up_read(&MSDOS_I(mapping->host)->truncate_lock);
>  
>  	return blocknr;
>  }
> @@ -510,6 +510,8 @@ static struct inode *fat_alloc_inode(str
>  	ei = kmem_cache_alloc(fat_inode_cachep, GFP_NOFS);
>  	if (!ei)
>  		return NULL;
> +
> +	init_rwsem(&ei->truncate_lock);
>  	return &ei->vfs_inode;
>  }
>  
> Index: linux-2.6/fs/fat/fat.h
> ===================================================================
> --- linux-2.6.orig/fs/fat/fat.h	2011-06-20 21:28:19.724630522 +0200
> +++ linux-2.6/fs/fat/fat.h	2011-06-20 21:29:25.034627215 +0200
> @@ -109,6 +109,7 @@ struct msdos_inode_info {
>  	int i_attrs;		/* unused attribute bits */
>  	loff_t i_pos;		/* on-disk position of directory entry or 0 */
>  	struct hlist_node i_fat_hash;	/* hash by i_location */
> +	struct rw_semaphore truncate_lock; /* protect bmap against truncate */
>  	struct inode vfs_inode;
>  };
>  
> Index: linux-2.6/fs/fat/file.c
> ===================================================================
> --- linux-2.6.orig/fs/fat/file.c	2011-06-20 21:28:19.744630521 +0200
> +++ linux-2.6/fs/fat/file.c	2011-06-20 21:29:54.501292390 +0200
> @@ -429,8 +429,10 @@ int fat_setattr(struct dentry *dentry, s
>  	}
>  
>  	if (attr->ia_valid & ATTR_SIZE) {
> +		down_write(&MSDOS_I(inode)->truncate_lock);
>  		truncate_setsize(inode, attr->ia_size);
>  		fat_truncate_blocks(inode, attr->ia_size);
> +		up_write(&MSDOS_I(inode)->truncate_lock);
>  	}
>  
>  	setattr_copy(inode, attr);
>
OGAWA Hirofumi - June 21, 2011, 4:09 p.m.
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes:

> Christoph Hellwig <hch@infradead.org> writes:
>
>> Add a new rw_semaphore to protect bmap against truncate.  Previous
>> i_alloc_sem was abused for this, but it's going away in this series.
>
> In FAT case, ->i_mutex was better. But, last time I saw, shmfs was using
> ->i_mutex to call ->bmap. So, this was chosen instead.
>
> I'm not checking current version yet though, if shmfs had change, we can
> use ->i_mutex.

It was swapfile. And unfortunately it doesn't have change.

> BTW, this patch looks good to me.
Christoph Hellwig - June 21, 2011, 4:09 p.m.
On Wed, Jun 22, 2011 at 12:57:43AM +0900, OGAWA Hirofumi wrote:
> Christoph Hellwig <hch@infradead.org> writes:
> 
> > Add a new rw_semaphore to protect bmap against truncate.  Previous
> > i_alloc_sem was abused for this, but it's going away in this series.
> 
> In FAT case, ->i_mutex was better. But, last time I saw, shmfs was using
> ->i_mutex to call ->bmap. So, this was chosen instead.
> 
> I'm not checking current version yet though, if shmfs had change, we can
> use ->i_mutex.

I tried that first, but it gives an instant deadlock when using a
swapfile on fat.

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Patch

Index: linux-2.6/fs/fat/inode.c
===================================================================
--- linux-2.6.orig/fs/fat/inode.c	2011-06-20 21:28:19.707963855 +0200
+++ linux-2.6/fs/fat/inode.c	2011-06-20 21:29:25.031293882 +0200
@@ -224,9 +224,9 @@  static sector_t _fat_bmap(struct address
 	sector_t blocknr;
 
 	/* fat_get_cluster() assumes the requested blocknr isn't truncated. */
-	down_read(&mapping->host->i_alloc_sem);
+	down_read(&MSDOS_I(mapping->host)->truncate_lock);
 	blocknr = generic_block_bmap(mapping, block, fat_get_block);
-	up_read(&mapping->host->i_alloc_sem);
+	up_read(&MSDOS_I(mapping->host)->truncate_lock);
 
 	return blocknr;
 }
@@ -510,6 +510,8 @@  static struct inode *fat_alloc_inode(str
 	ei = kmem_cache_alloc(fat_inode_cachep, GFP_NOFS);
 	if (!ei)
 		return NULL;
+
+	init_rwsem(&ei->truncate_lock);
 	return &ei->vfs_inode;
 }
 
Index: linux-2.6/fs/fat/fat.h
===================================================================
--- linux-2.6.orig/fs/fat/fat.h	2011-06-20 21:28:19.724630522 +0200
+++ linux-2.6/fs/fat/fat.h	2011-06-20 21:29:25.034627215 +0200
@@ -109,6 +109,7 @@  struct msdos_inode_info {
 	int i_attrs;		/* unused attribute bits */
 	loff_t i_pos;		/* on-disk position of directory entry or 0 */
 	struct hlist_node i_fat_hash;	/* hash by i_location */
+	struct rw_semaphore truncate_lock; /* protect bmap against truncate */
 	struct inode vfs_inode;
 };
 
Index: linux-2.6/fs/fat/file.c
===================================================================
--- linux-2.6.orig/fs/fat/file.c	2011-06-20 21:28:19.744630521 +0200
+++ linux-2.6/fs/fat/file.c	2011-06-20 21:29:54.501292390 +0200
@@ -429,8 +429,10 @@  int fat_setattr(struct dentry *dentry, s
 	}
 
 	if (attr->ia_valid & ATTR_SIZE) {
+		down_write(&MSDOS_I(inode)->truncate_lock);
 		truncate_setsize(inode, attr->ia_size);
 		fat_truncate_blocks(inode, attr->ia_size);
+		up_write(&MSDOS_I(inode)->truncate_lock);
 	}
 
 	setattr_copy(inode, attr);