On Wed, Mar 01, 2017 at 04:48:20PM +0800, Qu Wenruo wrote:
>
>
> At 03/01/2017 09:04 AM, Liu Bo wrote:
> > @pos, not aligned @start_pos, should be used to check whether the eof page
> > needs to be marked as readonly, thus @start_pos can be removed.
> >
> > Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> > ---
> > fs/btrfs/file.c | 7 +------
> > 1 file changed, 1 insertion(+), 6 deletions(-)
> >
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 0be837b..ef88e6d 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -1814,7 +1814,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> > struct inode *inode = file_inode(file);
> > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > struct btrfs_root *root = BTRFS_I(inode)->root;
> > - u64 start_pos;
> > u64 end_pos;
> > ssize_t num_written = 0;
> > bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
> > @@ -1822,7 +1821,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> > loff_t pos;
> > size_t count;
> > loff_t oldsize;
> > - int clean_page = 0;
> >
> > inode_lock(inode);
> > err = generic_write_checks(iocb, from);
> > @@ -1860,7 +1858,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> >
> > pos = iocb->ki_pos;
> > count = iov_iter_count(from);
> > - start_pos = round_down(pos, fs_info->sectorsize);
> > end_pos = round_up(pos + count, fs_info->sectorsize);
> > oldsize = i_size_read(inode);
> > if (end_pos > oldsize) {
> > @@ -1870,8 +1867,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> > inode_unlock(inode);
> > goto out;
> > }
> > - if (start_pos > round_up(oldsize, fs_info->sectorsize))
> > - clean_page = 1;
> > }
> >
> > if (sync)
> > @@ -1883,7 +1878,7 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> > num_written = __btrfs_buffered_write(file, from, pos);
> > if (num_written > 0)
> > iocb->ki_pos = pos + num_written;
> > - if (clean_page)
> > + if (oldsize < pos)
> > pagecache_isize_extended(inode, oldsize,
> > i_size_read(inode));
>
> Not familiar with page cache, so I can be totally wrong here.
>
> But what will happen if @oldsize and @pos are in the same page?
>
> For example:
> Page start Page start + 4K
> | | | |
> old size pos
>
> Do we still need to call pagecache_iszie_extented() since we will dirty that
> page anyway?
Yes, isize has changed, if blocksize < pagesize, so it's still possible that the
next write access to the new isize doesn't own an block since no page_mkwrite()
has been called to allocate it, then a following writepage() may fail silently
from userspace's view (unless they run fsync and check its ret).
Thanks,
-liubo
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