Messages in this thread | | | Date | Thu, 29 Aug 2013 18:27:11 +0200 | Subject | Re: [PATCH 1/2] fuse: postpone end_page_writeback() in fuse_writepage_locked() | From | Miklos Szeredi <> |
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On Mon, Aug 12, 2013 at 6:39 PM, Maxim Patlasov <MPatlasov@parallels.com> wrote: > The patch fixes a race between ftruncate(2), mmap-ed write and write(2): > > 1) An user makes a page dirty via mmap-ed write. > 2) The user performs shrinking truncate(2) intended to purge the page. > 3) Before fuse_do_setattr calls truncate_pagecache, the page goes to > writeback. fuse_writepage_locked fills FUSE_WRITE request and releases > the original page by end_page_writeback. > 4) fuse_do_setattr() completes and successfully returns. Since now, i_mutex > is free. > 5) Ordinary write(2) extends i_size back to cover the page. Note that > fuse_send_write_pages do wait for fuse writeback, but for another > page->index. > 6) fuse_writepage_locked proceeds by queueing FUSE_WRITE request. > fuse_send_writepage is supposed to crop inarg->size of the request, > but it doesn't because i_size has already been extended back. > > Moving end_page_writeback to the end of fuse_writepage_locked fixes the race > because now the fact that truncate_pagecache is successfully returned infers > that fuse_writepage_locked has already called end_page_writeback. And this, > in turn, infers that fuse_flush_writepages has already called > fuse_send_writepage, and the latter used valid (shrunk) i_size. write(2) > could not extend it because of i_mutex held by ftruncate(2). > > Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Applied this, too.
Thanks, Miklos
> --- > fs/fuse/file.c | 3 ++- > 1 files changed, 2 insertions(+), 1 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 5c121fe..d1715b3 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1529,7 +1529,6 @@ static int fuse_writepage_locked(struct page *page) > > inc_bdi_stat(mapping->backing_dev_info, BDI_WRITEBACK); > inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP); > - end_page_writeback(page); > > spin_lock(&fc->lock); > list_add(&req->writepages_entry, &fi->writepages); > @@ -1537,6 +1536,8 @@ static int fuse_writepage_locked(struct page *page) > fuse_flush_writepages(inode); > spin_unlock(&fc->lock); > > + end_page_writeback(page); > + > return 0; > > err_free: >
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