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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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