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SubjectRe: [PATCH 2/2] fuse: wait for writeback in fuse_file_fallocate() -v2
On 08/16/2013 07:30 AM, Maxim Patlasov wrote:
> The patch fixes a race between mmap-ed write and fallocate(PUNCH_HOLE):
>
> 1) An user makes a page dirty via mmap-ed write.
> 2) The user performs fallocate(2) with mode == PUNCH_HOLE|KEEP_SIZE
> and <offset, size> covering the page.
> 3) Before truncate_pagecache_range call from fuse_file_fallocate,
> the page goes to write-back. The page is fully processed by fuse_writepage
> (including end_page_writeback on the page), but fuse_flush_writepages did
> nothing because fi->writectr < 0.
> 4) truncate_pagecache_range is called and fuse_file_fallocate is finishing
> by calling fuse_release_nowrite. The latter triggers processing queued
> write-back request which will write stale data to the hole soon.
>
> Changed in v2 (thanks to Brian for suggestion):
> - Do not truncate page cache until FUSE_FALLOCATE succeeded. Otherwise,
> we can end up in returning -ENOTSUPP while user data is already punched
> from page cache. Use filemap_write_and_wait_range() instead.
>
> Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
> ---

Looks good to me, thanks Maxim.

Reviewed-by: Brian Foster <bfoster@redhat.com>

> fs/fuse/file.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 files changed, 48 insertions(+), 6 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index d1715b3..e88ba8b 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -344,6 +344,31 @@ static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
> return found;
> }
>
> +static bool fuse_range_is_writeback(struct inode *inode, pgoff_t idx_from,
> + pgoff_t idx_to)
> +{
> + struct fuse_conn *fc = get_fuse_conn(inode);
> + struct fuse_inode *fi = get_fuse_inode(inode);
> + struct fuse_req *req;
> + bool found = false;
> +
> + spin_lock(&fc->lock);
> + list_for_each_entry(req, &fi->writepages, writepages_entry) {
> + pgoff_t curr_index;
> +
> + BUG_ON(req->inode != inode);
> + curr_index = req->misc.write.in.offset >> PAGE_CACHE_SHIFT;
> + if (!(idx_from >= curr_index + req->num_pages ||
> + idx_to < curr_index)) {
> + found = true;
> + break;
> + }
> + }
> + spin_unlock(&fc->lock);
> +
> + return found;
> +}
> +
> /*
> * Wait for page writeback to be completed.
> *
> @@ -358,6 +383,19 @@ static int fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index)
> return 0;
> }
>
> +static void fuse_wait_on_writeback(struct inode *inode, pgoff_t start,
> + size_t bytes)
> +{
> + struct fuse_inode *fi = get_fuse_inode(inode);
> + pgoff_t idx_from, idx_to;
> +
> + idx_from = start >> PAGE_CACHE_SHIFT;
> + idx_to = (start + bytes - 1) >> PAGE_CACHE_SHIFT;
> +
> + wait_event(fi->page_waitq,
> + !fuse_range_is_writeback(inode, idx_from, idx_to));
> +}
> +
> static int fuse_flush(struct file *file, fl_owner_t id)
> {
> struct inode *inode = file_inode(file);
> @@ -2478,8 +2516,15 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
>
> if (lock_inode) {
> mutex_lock(&inode->i_mutex);
> - if (mode & FALLOC_FL_PUNCH_HOLE)
> - fuse_set_nowrite(inode);
> + if (mode & FALLOC_FL_PUNCH_HOLE) {
> + loff_t endbyte = offset + length - 1;
> + err = filemap_write_and_wait_range(inode->i_mapping,
> + offset, endbyte);
> + if (err)
> + goto out;
> +
> + fuse_wait_on_writeback(inode, offset, length);
> + }
> }
>
> req = fuse_get_req_nopages(fc);
> @@ -2514,11 +2559,8 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
> fuse_invalidate_attr(inode);
>
> out:
> - if (lock_inode) {
> - if (mode & FALLOC_FL_PUNCH_HOLE)
> - fuse_release_nowrite(inode);
> + if (lock_inode)
> mutex_unlock(&inode->i_mutex);
> - }
>
> return err;
> }
>



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