On Mon, 20 Jun 2011, Christoph Hellwig wrote:
> Add a new rw_semaphore to protect page_mkwrite against truncate. Previous
> i_alloc_sem was abused for this, but it's going away in this series.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
>
> Index: linux-2.6/fs/ext4/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/inode.c 2011-06-20 14:25:33.779248128 +0200
> +++ linux-2.6/fs/ext4/inode.c 2011-06-20 14:27:53.025907745 +0200
> @@ -5357,6 +5357,7 @@ int ext4_setattr(struct dentry *dentry,
> if (attr->ia_size > sbi->s_bitmap_maxbytes)
> return -EFBIG;
> }
> + down_write(&(EXT4_I(inode)->truncate_lock));
> }
>
> if (S_ISREG(inode->i_mode) &&
> @@ -5405,6 +5406,9 @@ int ext4_setattr(struct dentry *dentry,
> ext4_truncate(inode);
> }
>
> + if (attr->ia_valid & ATTR_SIZE)
> + up_write(&(EXT4_I(inode)->truncate_lock));
> +
Hi Christoph,
this looks like a bug fix, so we should rather do it in a separate
commit. Could you send it separately, or at least mention that in commit
description ?
Otherwise the patch looks good.
Thanks!
-Lukas
> if (!rc) {
> setattr_copy(inode, attr);
> mark_inode_dirty(inode);
> @@ -5850,10 +5854,10 @@ int ext4_page_mkwrite(struct vm_area_str
> struct address_space *mapping = inode->i_mapping;
>
> /*
> - * Get i_alloc_sem to stop truncates messing with the inode. We cannot
> - * get i_mutex because we are already holding mmap_sem.
> + * Get truncate_lock to stop truncates messing with the inode. We
> + * cannot get i_mutex because we are already holding mmap_sem.
> */
> - down_read(&inode->i_alloc_sem);
> + down_read(&(EXT4_I(inode)->truncate_lock));
> size = i_size_read(inode);
> if (page->mapping != mapping || size <= page_offset(page)
> || !PageUptodate(page)) {
> @@ -5865,7 +5869,7 @@ int ext4_page_mkwrite(struct vm_area_str
> lock_page(page);
> wait_on_page_writeback(page);
> if (PageMappedToDisk(page)) {
> - up_read(&inode->i_alloc_sem);
> + up_read(&(EXT4_I(inode)->truncate_lock));
> return VM_FAULT_LOCKED;
> }
>
> @@ -5883,7 +5887,7 @@ int ext4_page_mkwrite(struct vm_area_str
> if (page_has_buffers(page)) {
> if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
> ext4_bh_unmapped)) {
> - up_read(&inode->i_alloc_sem);
> + up_read(&(EXT4_I(inode)->truncate_lock));
> return VM_FAULT_LOCKED;
> }
> }
> @@ -5912,11 +5916,11 @@ int ext4_page_mkwrite(struct vm_area_str
> */
> lock_page(page);
> wait_on_page_writeback(page);
> - up_read(&inode->i_alloc_sem);
> + up_read(&(EXT4_I(inode)->truncate_lock));
> return VM_FAULT_LOCKED;
> out_unlock:
> if (ret)
> ret = VM_FAULT_SIGBUS;
> - up_read(&inode->i_alloc_sem);
> + up_read(&(EXT4_I(inode)->truncate_lock));
> return ret;
> }
> Index: linux-2.6/fs/ext4/super.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/super.c 2011-06-20 14:25:33.795914793 +0200
> +++ linux-2.6/fs/ext4/super.c 2011-06-20 14:27:06.269243443 +0200
> @@ -871,6 +871,7 @@ static struct inode *ext4_alloc_inode(st
> ei->i_datasync_tid = 0;
> atomic_set(&ei->i_ioend_count, 0);
> atomic_set(&ei->i_aiodio_unwritten, 0);
> + init_rwsem(&ei->truncate_lock);
>
> return &ei->vfs_inode;
> }
> Index: linux-2.6/fs/ext4/ext4.h
> ===================================================================
> --- linux-2.6.orig/fs/ext4/ext4.h 2011-06-20 14:25:33.752581461 +0200
> +++ linux-2.6/fs/ext4/ext4.h 2011-06-20 14:27:06.272576777 +0200
> @@ -844,6 +844,9 @@ struct ext4_inode_info {
> /* on-disk additional length */
> __u16 i_extra_isize;
>
> + /* protect page_mkwrite against truncates */
> + struct rw_semaphore truncate_lock;
> +
> #ifdef CONFIG_QUOTA
> /* quota space reservation, managed internally by quota code */
> qsize_t i_reserved_quota;
>
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