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 6b35fc4860a0381ab33ccc6162ca5184555373b6..1de16a5a5c4ee7418a4881377a7993cf6ef8885d 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                goto superseded;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-               goto superseded;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 superseded: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 */