fuse: release pipe buf after last use

Origin: https://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git/commit/?h=for-next&id=473441720c8616dfaf4451f9c7ea14f0eb5e5d65
Bug-Debian: https://bugs.debian.org/1000504

Checking buf->flags should be done before the pipe_buf_release() is called
on the pipe buffer, since releasing the buffer might modify the flags.

This is exactly what page_cache_pipe_buf_release() does, and which results
in the same VM_BUG_ON_PAGE(PageLRU(page)) that the original patch was
trying to fix.

Reported-by: Justin Forbes <jmforbes@linuxtx.org>
Fixes: 712a951025c0 ("fuse: fix page stealing")
Cc: <stable@vger.kernel.org> # v2.6.35
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name fuse-release-pipe-buf-after-last-use.patch

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 5a1f142bdb4845a92672dc29056e4c88f793ddde..a9d21b33da9c4552f619cd2e91b49c8513a7db64 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -847,17 +847,17 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
 
        replace_page_cache_page(oldpage, newpage);
 
+       get_page(newpage);
+
+       if (!(buf->flags & PIPE_BUF_FLAG_LRU))
+               lru_cache_add(newpage);
+
        /*
         * Release while we have extra ref on stolen page.  Otherwise
         * anon_pipe_buf_release() might think the page can be reused.
         */
        pipe_buf_release(cs->pipe, buf);
 
-       get_page(newpage);
-
-       if (!(buf->flags & PIPE_BUF_FLAG_LRU))
-               lru_cache_add(newpage);
-
        err = 0;
        spin_lock(&cs->req->waitq.lock);
        if (test_bit(FR_ABORTED, &cs->req->flags))