linux-kernel - Re: [PATCH] fs: btrfs: Change return type to vm_fault

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Date:   Wed, 6 Jun 2018 19:39:53 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     dsterba@...e.cz, Souptick Joarder <jrdr.linux@...il.com>,
        Matthew Wilcox <willy@...radead.org>, Chris Mason <clm@...com>,
        jbacik@...com, dsterba@...e.com, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: btrfs: Change return type to vm_fault_t

On Wed, Jun 6, 2018 at 6:52 PM, David Sterba <dsterba@...e.cz> wrote:
> On Tue, Jun 05, 2018 at 09:16:35PM +0530, Souptick Joarder wrote:
>> Use new return type vm_fault_t for fault handler. For
>> now, this is just documenting that the function returns
>> a VM_FAULT value rather than an errno. Once all instances
>> are converted, vm_fault_t will become a distinct type.
>>
>> Ref-> commit 1c8f422059ae ("mm: change return type to vm_fault_t")
>>
>> vmf_error() is the newly introduce inline function
>> in 4.17-rc6.
>>
>> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
>> ---
>>  fs/btrfs/ctree.h |  2 +-
>>  fs/btrfs/inode.c | 28 +++++++++++++---------------
>>  2 files changed, 14 insertions(+), 16 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index 0d422c9..1f52d9fd 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -3218,7 +3218,7 @@ int btrfs_merge_bio_hook(struct page *page, unsigned long offset,
>>                        size_t size, struct bio *bio,
>>                        unsigned long bio_flags);
>>  void btrfs_set_range_writeback(void *private_data, u64 start, u64 end);
>> -int btrfs_page_mkwrite(struct vm_fault *vmf);
>> +vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf);
>>  int btrfs_readpage(struct file *file, struct page *page);
>>  void btrfs_evict_inode(struct inode *inode);
>>  int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc);
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index 0b86cf1..20bde86 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -8873,7 +8873,7 @@ static void btrfs_invalidatepage(struct page *page, unsigned int offset,
>>   * beyond EOF, then the page is guaranteed safe against truncation until we
>>   * unlock the page.
>>   */
>> -int btrfs_page_mkwrite(struct vm_fault *vmf)
>> +vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
>>  {
>>       struct page *page = vmf->page;
>>       struct inode *inode = file_inode(vmf->vma->vm_file);
>> @@ -8885,8 +8885,9 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
>>       char *kaddr;
>>       unsigned long zero_start;
>>       loff_t size;
>> -     int ret;
>> +     int err;
>
> Please use ret2 for the variable name. We're leaving the err/ret naming
> pattern and use 'ret' to match the function return value and ret2, ret3
> for the temporary return values.

Is this new pattern specific to fs/btrfs file system ?
>
>>       int reserved = 0;
>> +     vm_fault_t ret;
>>       u64 reserved_space;
>>       u64 page_start;
>>       u64 page_end;
>> @@ -8907,17 +8908,14 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
>>        * end up waiting indefinitely to get a lock on the page currently
>>        * being processed by btrfs_page_mkwrite() function.
>>        */
>> -     ret = btrfs_delalloc_reserve_space(inode, &data_reserved, page_start,
>> +     err = btrfs_delalloc_reserve_space(inode, &data_reserved, page_start,
>>                                          reserved_space);
>> -     if (!ret) {
>> -             ret = file_update_time(vmf->vma->vm_file);
>> +     if (!err) {
>> +             err = file_update_time(vmf->vma->vm_file);
>>               reserved = 1;
>>       }
>> -     if (ret) {
>> -             if (ret == -ENOMEM)
>> -                     ret = VM_FAULT_OOM;
>> -             else /* -ENOSPC, -EIO, etc */
>> -                     ret = VM_FAULT_SIGBUS;
>> +     if (err) {
>> +             ret = vmf_error(err);
>>               if (reserved)
>>                       goto out;
>>               goto out_noreserve;
>> @@ -8976,15 +8974,15 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
>>                         EXTENT_DO_ACCOUNTING | EXTENT_DEFRAG,
>>                         0, 0, &cached_state);
>>
>> -     ret = btrfs_set_extent_delalloc(inode, page_start, end, 0,
>> +     err = btrfs_set_extent_delalloc(inode, page_start, end, 0,
>>                                       &cached_state, 0);
>> -     if (ret) {
>> +     if (err) {
>>               unlock_extent_cached(io_tree, page_start, page_end,
>>                                    &cached_state);
>>               ret = VM_FAULT_SIGBUS;
>>               goto out_unlock;
>>       }
>> -     ret = 0;
>> +     err = 0;
>>
>>       /* page is wholly or partially inside EOF */
>>       if (page_start + PAGE_SIZE > size)
>> @@ -9009,11 +9007,11 @@ int btrfs_page_mkwrite(struct vm_fault *vmf)
>>       unlock_extent_cached(io_tree, page_start, page_end, &cached_state);
>>
>>  out_unlock:
>> -     if (!ret) {
>> +     if (!err) {
>>               btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, true);
>>               sb_end_pagefault(inode->i_sb);
>>               extent_changeset_free(data_reserved);
>> -             return VM_FAULT_LOCKED;
>> +             ret = VM_FAULT_LOCKED;
>
> That's not a direct change as it changes the code flow and lets the
> branch continue. As the error handling and cleanup code is partially
> done in this branch continuing wrong AFAICS.

Sorry about it, I will correct and send v2.
Is it possible to get it merge in 4.18 / 4.18-rc-X ?