On Wed 27-01-16 12:01:48, Ross Zwisler wrote:
> As it is currently written ext4_dax_mkwrite() assumes that the call into
> __dax_mkwrite() will not have to do a block allocation so it doesn't create
> a journal entry. For a read that creates a zero page to cover a hole
> followed by a write that actually allocates storage this is incorrect. The
> ext4_dax_mkwrite() -> __dax_mkwrite() -> __dax_fault() path calls
> get_blocks() to allocate storage.
>
> Fix this by having the ->page_mkwrite fault handler call ext4_dax_fault()
> as this function already has all the logic needed to allocate a journal
> entry and call __dax_fault().
>
> Also update the ext2 fault handlers in this same way to remove duplicate
> code and keep the logic between ext2 and ext4 the same.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Ah, ok, you are right. The patch looks good but Matthew is reworking the
area more (so ext4_da_mkwrite() is likely to return) so it this worth it?
Or do you expect Matthew's patches to land much later?
Honza
> ---
> fs/ext2/file.c | 19 +------------------
> fs/ext4/file.c | 19 ++-----------------
> 2 files changed, 3 insertions(+), 35 deletions(-)
>
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index 2c88d68..c1400b1 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -80,23 +80,6 @@ static int ext2_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> return ret;
> }
>
> -static int ext2_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> -{
> - struct inode *inode = file_inode(vma->vm_file);
> - struct ext2_inode_info *ei = EXT2_I(inode);
> - int ret;
> -
> - sb_start_pagefault(inode->i_sb);
> - file_update_time(vma->vm_file);
> - down_read(&ei->dax_sem);
> -
> - ret = __dax_mkwrite(vma, vmf, ext2_get_block, NULL);
> -
> - up_read(&ei->dax_sem);
> - sb_end_pagefault(inode->i_sb);
> - return ret;
> -}
> -
> static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
> struct vm_fault *vmf)
> {
> @@ -124,7 +107,7 @@ static int ext2_dax_pfn_mkwrite(struct vm_area_struct *vma,
> static const struct vm_operations_struct ext2_dax_vm_ops = {
> .fault = ext2_dax_fault,
> .pmd_fault = ext2_dax_pmd_fault,
> - .page_mkwrite = ext2_dax_mkwrite,
> + .page_mkwrite = ext2_dax_fault,
> .pfn_mkwrite = ext2_dax_pfn_mkwrite,
> };
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 1126436..d2e8500 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -262,23 +262,8 @@ static int ext4_dax_pmd_fault(struct vm_area_struct *vma, unsigned long addr,
> return result;
> }
>
> -static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> -{
> - int err;
> - struct inode *inode = file_inode(vma->vm_file);
> -
> - sb_start_pagefault(inode->i_sb);
> - file_update_time(vma->vm_file);
> - down_read(&EXT4_I(inode)->i_mmap_sem);
> - err = __dax_mkwrite(vma, vmf, ext4_dax_mmap_get_block, NULL);
> - up_read(&EXT4_I(inode)->i_mmap_sem);
> - sb_end_pagefault(inode->i_sb);
> -
> - return err;
> -}
> -
> /*
> - * Handle write fault for VM_MIXEDMAP mappings. Similarly to ext4_dax_mkwrite()
> + * Handle write fault for VM_MIXEDMAP mappings. Similarly to ext4_dax_fault()
> * handler we check for races agaist truncate. Note that since we cycle through
> * i_mmap_sem, we are sure that also any hole punching that began before we
> * were called is finished by now and so if it included part of the file we
> @@ -311,7 +296,7 @@ static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma,
> static const struct vm_operations_struct ext4_dax_vm_ops = {
> .fault = ext4_dax_fault,
> .pmd_fault = ext4_dax_pmd_fault,
> - .page_mkwrite = ext4_dax_mkwrite,
> + .page_mkwrite = ext4_dax_fault,
> .pfn_mkwrite = ext4_dax_pfn_mkwrite,
> };
> #else
> --
> 2.5.0
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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