Re: [PATCH 05/14] ext4: Convert to use mapping->invalidate_lock

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Jun 15, 2021 at 11:17:55AM +0200, Jan Kara wrote:
> Convert ext4 to use mapping->invalidate_lock instead of its private
> EXT4_I(inode)->i_mmap_sem. This is mostly search-and-replace. By this
> conversion we fix a long standing race between hole punching and read(2)
> / readahead(2) paths that can lead to stale page cache contents.
> 
> CC: <linux-ext4@vger.kernel.org>
> CC: Ted Tso <tytso@mit.edu>

Hmm, still no ACK from Ted?

This looks like a pretty straightforward i_mmap_sem conversion, though
in general I'd like /some/ kind of response from anyone in the ext4
community who has been writing code more recently than me...

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/ext4/ext4.h     | 10 ----------
>  fs/ext4/extents.c  | 25 +++++++++++++-----------
>  fs/ext4/file.c     | 13 +++++++------
>  fs/ext4/inode.c    | 47 +++++++++++++++++-----------------------------
>  fs/ext4/ioctl.c    |  4 ++--
>  fs/ext4/super.c    | 13 +++++--------
>  fs/ext4/truncate.h |  8 +++++---
>  7 files changed, 50 insertions(+), 70 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 37002663d521..ed64b4b217a1 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1077,15 +1077,6 @@ struct ext4_inode_info {
>  	 * by other means, so we have i_data_sem.
>  	 */
>  	struct rw_semaphore i_data_sem;
> -	/*
> -	 * i_mmap_sem is for serializing page faults with truncate / punch hole
> -	 * operations. We have to make sure that new page cannot be faulted in
> -	 * a section of the inode that is being punched. We cannot easily use
> -	 * i_data_sem for this since we need protection for the whole punch
> -	 * operation and i_data_sem ranks below transaction start so we have
> -	 * to occasionally drop it.
> -	 */
> -	struct rw_semaphore i_mmap_sem;
>  	struct inode vfs_inode;
>  	struct jbd2_inode *jinode;
>  
> @@ -2962,7 +2953,6 @@ extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
>  extern int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
>  			     loff_t lstart, loff_t lend);
>  extern vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf);
> -extern vm_fault_t ext4_filemap_fault(struct vm_fault *vmf);
>  extern qsize_t *ext4_get_reserved_space(struct inode *inode);
>  extern int ext4_get_projid(struct inode *inode, kprojid_t *projid);
>  extern void ext4_da_release_space(struct inode *inode, int to_free);
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index cbf37b2cf871..db5d38af9ba8 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4470,6 +4470,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  			    loff_t len, int mode)
>  {
>  	struct inode *inode = file_inode(file);
> +	struct address_space *mapping = file->f_mapping;
>  	handle_t *handle = NULL;
>  	unsigned int max_blocks;
>  	loff_t new_size = 0;
> @@ -4556,17 +4557,17 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  		 * Prevent page faults from reinstantiating pages we have
>  		 * released from page cache.
>  		 */
> -		down_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_lock(mapping);
>  
>  		ret = ext4_break_layouts(inode);
>  		if (ret) {
> -			up_write(&EXT4_I(inode)->i_mmap_sem);
> +			filemap_invalidate_unlock(mapping);
>  			goto out_mutex;
>  		}
>  
>  		ret = ext4_update_disksize_before_punch(inode, offset, len);
>  		if (ret) {
> -			up_write(&EXT4_I(inode)->i_mmap_sem);
> +			filemap_invalidate_unlock(mapping);
>  			goto out_mutex;
>  		}
>  		/* Now release the pages and zero block aligned part of pages */
> @@ -4575,7 +4576,7 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  
>  		ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size,
>  					     flags);
> -		up_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_unlock(mapping);
>  		if (ret)
>  			goto out_mutex;
>  	}
> @@ -5217,6 +5218,7 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle,
>  static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  {
>  	struct super_block *sb = inode->i_sb;
> +	struct address_space *mapping = inode->i_mapping;
>  	ext4_lblk_t punch_start, punch_stop;
>  	handle_t *handle;
>  	unsigned int credits;
> @@ -5270,7 +5272,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  	 * Prevent page faults from reinstantiating pages we have released from
>  	 * page cache.
>  	 */
> -	down_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_lock(mapping);
>  
>  	ret = ext4_break_layouts(inode);
>  	if (ret)
> @@ -5285,15 +5287,15 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  	 * Write tail of the last page before removed range since it will get
>  	 * removed from the page cache below.
>  	 */
> -	ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, offset);
> +	ret = filemap_write_and_wait_range(mapping, ioffset, offset);
>  	if (ret)
>  		goto out_mmap;
>  	/*
>  	 * Write data that will be shifted to preserve them when discarding
>  	 * page cache below. We are also protected from pages becoming dirty
> -	 * by i_mmap_sem.
> +	 * by i_rwsem and invalidate_lock.
>  	 */
> -	ret = filemap_write_and_wait_range(inode->i_mapping, offset + len,
> +	ret = filemap_write_and_wait_range(mapping, offset + len,
>  					   LLONG_MAX);
>  	if (ret)
>  		goto out_mmap;
> @@ -5346,7 +5348,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  	ext4_journal_stop(handle);
>  	ext4_fc_stop_ineligible(sb);
>  out_mmap:
> -	up_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_unlock(mapping);
>  out_mutex:
>  	inode_unlock(inode);
>  	return ret;
> @@ -5363,6 +5365,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  static int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
>  {
>  	struct super_block *sb = inode->i_sb;
> +	struct address_space *mapping = inode->i_mapping;
>  	handle_t *handle;
>  	struct ext4_ext_path *path;
>  	struct ext4_extent *extent;
> @@ -5421,7 +5424,7 @@ static int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
>  	 * Prevent page faults from reinstantiating pages we have released from
>  	 * page cache.
>  	 */
> -	down_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_lock(mapping);
>  
>  	ret = ext4_break_layouts(inode);
>  	if (ret)
> @@ -5522,7 +5525,7 @@ static int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
>  	ext4_journal_stop(handle);
>  	ext4_fc_stop_ineligible(sb);
>  out_mmap:
> -	up_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_unlock(mapping);
>  out_mutex:
>  	inode_unlock(inode);
>  	return ret;
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 816dedcbd541..d3b4ed91aa68 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -704,22 +704,23 @@ static vm_fault_t ext4_dax_huge_fault(struct vm_fault *vmf,
>  	 */
>  	bool write = (vmf->flags & FAULT_FLAG_WRITE) &&
>  		(vmf->vma->vm_flags & VM_SHARED);
> +	struct address_space *mapping = vmf->vma->vm_file->f_mapping;
>  	pfn_t pfn;
>  
>  	if (write) {
>  		sb_start_pagefault(sb);
>  		file_update_time(vmf->vma->vm_file);
> -		down_read(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_lock_shared(mapping);
>  retry:
>  		handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE,
>  					       EXT4_DATA_TRANS_BLOCKS(sb));
>  		if (IS_ERR(handle)) {
> -			up_read(&EXT4_I(inode)->i_mmap_sem);
> +			filemap_invalidate_unlock_shared(mapping);
>  			sb_end_pagefault(sb);
>  			return VM_FAULT_SIGBUS;
>  		}
>  	} else {
> -		down_read(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_lock_shared(mapping);
>  	}
>  	result = dax_iomap_fault(vmf, pe_size, &pfn, &error, &ext4_iomap_ops);
>  	if (write) {
> @@ -731,10 +732,10 @@ static vm_fault_t ext4_dax_huge_fault(struct vm_fault *vmf,
>  		/* Handling synchronous page fault? */
>  		if (result & VM_FAULT_NEEDDSYNC)
>  			result = dax_finish_sync_fault(vmf, pe_size, pfn);
> -		up_read(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_unlock_shared(mapping);
>  		sb_end_pagefault(sb);
>  	} else {
> -		up_read(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_unlock_shared(mapping);
>  	}
>  
>  	return result;
> @@ -756,7 +757,7 @@ static const struct vm_operations_struct ext4_dax_vm_ops = {
>  #endif
>  
>  static const struct vm_operations_struct ext4_file_vm_ops = {
> -	.fault		= ext4_filemap_fault,
> +	.fault		= filemap_fault,
>  	.map_pages	= filemap_map_pages,
>  	.page_mkwrite   = ext4_page_mkwrite,
>  };
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index fe6045a46599..ee6e69d6f949 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3950,20 +3950,19 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
>  	return ret;
>  }
>  
> -static void ext4_wait_dax_page(struct ext4_inode_info *ei)
> +static void ext4_wait_dax_page(struct inode *inode)
>  {
> -	up_write(&ei->i_mmap_sem);
> +	filemap_invalidate_unlock(inode->i_mapping);
>  	schedule();
> -	down_write(&ei->i_mmap_sem);
> +	filemap_invalidate_lock(inode->i_mapping);
>  }
>  
>  int ext4_break_layouts(struct inode *inode)
>  {
> -	struct ext4_inode_info *ei = EXT4_I(inode);
>  	struct page *page;
>  	int error;
>  
> -	if (WARN_ON_ONCE(!rwsem_is_locked(&ei->i_mmap_sem)))
> +	if (WARN_ON_ONCE(!rwsem_is_locked(&inode->i_mapping->invalidate_lock)))
>  		return -EINVAL;
>  
>  	do {
> @@ -3974,7 +3973,7 @@ int ext4_break_layouts(struct inode *inode)
>  		error = ___wait_var_event(&page->_refcount,
>  				atomic_read(&page->_refcount) == 1,
>  				TASK_INTERRUPTIBLE, 0, 0,
> -				ext4_wait_dax_page(ei));
> +				ext4_wait_dax_page(inode));
>  	} while (error == 0);
>  
>  	return error;
> @@ -4005,9 +4004,9 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
>  
>  	ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
>  	if (ext4_has_inline_data(inode)) {
> -		down_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_lock(mapping);
>  		ret = ext4_convert_inline_data(inode);
> -		up_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_unlock(mapping);
>  		if (ret)
>  			return ret;
>  	}
> @@ -4058,7 +4057,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
>  	 * Prevent page faults from reinstantiating pages we have released from
>  	 * page cache.
>  	 */
> -	down_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_lock(mapping);
>  
>  	ret = ext4_break_layouts(inode);
>  	if (ret)
> @@ -4131,7 +4130,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
>  out_stop:
>  	ext4_journal_stop(handle);
>  out_dio:
> -	up_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_unlock(mapping);
>  out_mutex:
>  	inode_unlock(inode);
>  	return ret;
> @@ -5426,11 +5425,11 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>  			inode_dio_wait(inode);
>  		}
>  
> -		down_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_lock(inode->i_mapping);
>  
>  		rc = ext4_break_layouts(inode);
>  		if (rc) {
> -			up_write(&EXT4_I(inode)->i_mmap_sem);
> +			filemap_invalidate_unlock(inode->i_mapping);
>  			goto err_out;
>  		}
>  
> @@ -5506,7 +5505,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>  				error = rc;
>  		}
>  out_mmap_sem:
> -		up_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_unlock(inode->i_mapping);
>  	}
>  
>  	if (!error) {
> @@ -5983,10 +5982,10 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
>  	 * data (and journalled aops don't know how to handle these cases).
>  	 */
>  	if (val) {
> -		down_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_lock(inode->i_mapping);
>  		err = filemap_write_and_wait(inode->i_mapping);
>  		if (err < 0) {
> -			up_write(&EXT4_I(inode)->i_mmap_sem);
> +			filemap_invalidate_unlock(inode->i_mapping);
>  			return err;
>  		}
>  	}
> @@ -6019,7 +6018,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
>  	percpu_up_write(&sbi->s_writepages_rwsem);
>  
>  	if (val)
> -		up_write(&EXT4_I(inode)->i_mmap_sem);
> +		filemap_invalidate_unlock(inode->i_mapping);
>  
>  	/* Finally we can mark the inode as dirty. */
>  
> @@ -6063,7 +6062,7 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>  	sb_start_pagefault(inode->i_sb);
>  	file_update_time(vma->vm_file);
>  
> -	down_read(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_lock_shared(mapping);
>  
>  	err = ext4_convert_inline_data(inode);
>  	if (err)
> @@ -6176,7 +6175,7 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>  out_ret:
>  	ret = block_page_mkwrite_return(err);
>  out:
> -	up_read(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_unlock_shared(mapping);
>  	sb_end_pagefault(inode->i_sb);
>  	return ret;
>  out_error:
> @@ -6184,15 +6183,3 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>  	ext4_journal_stop(handle);
>  	goto out;
>  }
> -
> -vm_fault_t ext4_filemap_fault(struct vm_fault *vmf)
> -{
> -	struct inode *inode = file_inode(vmf->vma->vm_file);
> -	vm_fault_t ret;
> -
> -	down_read(&EXT4_I(inode)->i_mmap_sem);
> -	ret = filemap_fault(vmf);
> -	up_read(&EXT4_I(inode)->i_mmap_sem);
> -
> -	return ret;
> -}
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 31627f7dc5cd..c5ed562b4185 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -148,7 +148,7 @@ static long swap_inode_boot_loader(struct super_block *sb,
>  		goto journal_err_out;
>  	}
>  
> -	down_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_lock(inode->i_mapping);
>  	err = filemap_write_and_wait(inode->i_mapping);
>  	if (err)
>  		goto err_out;
> @@ -256,7 +256,7 @@ static long swap_inode_boot_loader(struct super_block *sb,
>  	ext4_double_up_write_data_sem(inode, inode_bl);
>  
>  err_out:
> -	up_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_unlock(inode->i_mapping);
>  journal_err_out:
>  	unlock_two_nondirectories(inode, inode_bl);
>  	iput(inode_bl);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d29f6aa7d96e..c3c3cd8b0966 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -90,12 +90,9 @@ static struct inode *ext4_get_journal_inode(struct super_block *sb,
>  /*
>   * Lock ordering
>   *
> - * Note the difference between i_mmap_sem (EXT4_I(inode)->i_mmap_sem) and
> - * i_mmap_rwsem (inode->i_mmap_rwsem)!
> - *
>   * page fault path:
> - * mmap_lock -> sb_start_pagefault -> i_mmap_sem (r) -> transaction start ->
> - *   page lock -> i_data_sem (rw)
> + * mmap_lock -> sb_start_pagefault -> invalidate_lock (r) -> transaction start
> + *   -> page lock -> i_data_sem (rw)
>   *
>   * buffered write path:
>   * sb_start_write -> i_mutex -> mmap_lock
> @@ -103,8 +100,9 @@ static struct inode *ext4_get_journal_inode(struct super_block *sb,
>   *   i_data_sem (rw)
>   *
>   * truncate:
> - * sb_start_write -> i_mutex -> i_mmap_sem (w) -> i_mmap_rwsem (w) -> page lock
> - * sb_start_write -> i_mutex -> i_mmap_sem (w) -> transaction start ->
> + * sb_start_write -> i_mutex -> invalidate_lock (w) -> i_mmap_rwsem (w) ->
> + *   page lock
> + * sb_start_write -> i_mutex -> invalidate_lock (w) -> transaction start ->
>   *   i_data_sem (rw)
>   *
>   * direct IO:
> @@ -1350,7 +1348,6 @@ static void init_once(void *foo)
>  	INIT_LIST_HEAD(&ei->i_orphan);
>  	init_rwsem(&ei->xattr_sem);
>  	init_rwsem(&ei->i_data_sem);
> -	init_rwsem(&ei->i_mmap_sem);
>  	inode_init_once(&ei->vfs_inode);
>  	ext4_fc_init_inode(&ei->vfs_inode);
>  }
> diff --git a/fs/ext4/truncate.h b/fs/ext4/truncate.h
> index bcbe3668c1d4..ce84aa2786c7 100644
> --- a/fs/ext4/truncate.h
> +++ b/fs/ext4/truncate.h
> @@ -11,14 +11,16 @@
>   */
>  static inline void ext4_truncate_failed_write(struct inode *inode)
>  {
> +	struct address_space *mapping = inode->i_mapping;
> +
>  	/*
>  	 * We don't need to call ext4_break_layouts() because the blocks we
>  	 * are truncating were never visible to userspace.
>  	 */
> -	down_write(&EXT4_I(inode)->i_mmap_sem);
> -	truncate_inode_pages(inode->i_mapping, inode->i_size);
> +	filemap_invalidate_lock(mapping);
> +	truncate_inode_pages(mapping, inode->i_size);
>  	ext4_truncate(inode);
> -	up_write(&EXT4_I(inode)->i_mmap_sem);
> +	filemap_invalidate_unlock(mapping);
>  }
>  
>  /*
> -- 
> 2.26.2
>