fscache: Fix hanging wait on page discarded by writeback

[ Upstream commit 2c98425720233ae3e135add0c7e869b32913502f ]

If the fscache asynchronous write operation elects to discard a page that's
pending storage to the cache because the page would be over the store limit
then it needs to wake the page as someone may be waiting on completion of
the write.

The problem is that the store limit may be updated by a different
asynchronous operation - and so may miss the write - and that the store
limit may not even get updated until later by the netfs.

Fix the kernel hang by making fscache_write_op() mark as written any pages
that are over the limit.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 0ad3fd3ad0b477c3e0ee2b74d4af78977e405f7b..ae9470f3643c243fab43650e1bd9cbaa6294811a 100644 (file)
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -776,6 +776,7 @@ static void fscache_write_op(struct fscache_operation *_op)
 
        _enter("{OP%x,%d}", op->op.debug_id, atomic_read(&op->op.usage));
 
+again:
        spin_lock(&object->lock);
        cookie = object->cookie;
 
@@ -816,10 +817,6 @@ static void fscache_write_op(struct fscache_operation *_op)
                goto superseded;
        page = results[0];
        _debug("gang %d [%lx]", n, page->index);
-       if (page->index >= op->store_limit) {
-               fscache_stat(&fscache_n_store_pages_over_limit);
-               goto superseded;
-       }
 
        radix_tree_tag_set(&cookie->stores, page->index,
                           FSCACHE_COOKIE_STORING_TAG);
@@ -829,6 +826,9 @@ static void fscache_write_op(struct fscache_operation *_op)
        spin_unlock(&cookie->stores_lock);
        spin_unlock(&object->lock);
 
+       if (page->index >= op->store_limit)
+               goto discard_page;
+
        fscache_stat(&fscache_n_store_pages);
        fscache_stat(&fscache_n_cop_write_page);
        ret = object->cache->ops->write_page(op, page);
@@ -844,6 +844,11 @@ static void fscache_write_op(struct fscache_operation *_op)
        _leave("");
        return;
 
+discard_page:
+       fscache_stat(&fscache_n_store_pages_over_limit);
+       fscache_end_page_write(object, page);
+       goto again;
+
 superseded:
        /* this writer is going away and there aren't any more things to
         * write */