linux-kernel - [PATCH 03/67] vfs, fscache: Force ->write_inode() to occur if cookie pinned for writeback

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Date:   Mon, 18 Oct 2021 15:51:05 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
Cc:     dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 03/67] vfs,
 fscache: Force ->write_inode() to occur if cookie pinned for writeback

Use an inode flag, I_PINNING_FSCACHE_WB, to indicate that a cookie is
pinned in use by that inode for the purposes of writeback.

Pinning is necessary because the in-use pin from the open file is released
before the writeback takes place, but if the resources aren't pinned, the
dirty data can't be written to the cache.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/fs-writeback.c         |    8 ++++++++
 include/linux/fs.h        |    3 +++
 include/linux/fscache.h   |    1 +
 include/linux/writeback.h |    1 +
 4 files changed, 13 insertions(+)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 81ec192ce067..f3122831c4fe 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1666,6 +1666,13 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 
 	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
 		inode->i_state |= I_DIRTY_PAGES;
+	else if (unlikely(inode->i_state & I_PINNING_FSCACHE_WB)) {
+		if (!(inode->i_state & I_DIRTY_PAGES)) {
+			inode->i_state &= ~I_PINNING_FSCACHE_WB;
+			wbc->unpinned_fscache_wb = true;
+			dirty |= I_PINNING_FSCACHE_WB; /* Cause write_inode */
+		}
+	}
 
 	spin_unlock(&inode->i_lock);
 
@@ -1675,6 +1682,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 		if (ret == 0)
 			ret = err;
 	}
+	wbc->unpinned_fscache_wb = false;
 	trace_writeback_single_inode(inode, wbc, nr_to_write);
 	return ret;
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 197493507744..336739fed3e9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2420,6 +2420,8 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
  *			Used to detect that mark_inode_dirty() should not move
  * 			inode between dirty lists.
  *
+ * I_PINNING_FSCACHE_WB	Inode is pinning an fscache object for writeback.
+ *
  * Q: What is the difference between I_WILL_FREE and I_FREEING?
  */
 #define I_DIRTY_SYNC		(1 << 0)
@@ -2442,6 +2444,7 @@ static inline void kiocb_clone(struct kiocb *kiocb, struct kiocb *kiocb_src,
 #define I_CREATING		(1 << 15)
 #define I_DONTCACHE		(1 << 16)
 #define I_SYNC_QUEUED		(1 << 17)
+#define I_PINNING_FSCACHE_WB	(1 << 18)
 
 #define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC)
 #define I_DIRTY (I_DIRTY_INODE | I_DIRTY_PAGES)
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 01558d155799..ba4878b56717 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -19,6 +19,7 @@
 #include <linux/pagemap.h>
 #include <linux/pagevec.h>
 #include <linux/list_bl.h>
+#include <linux/writeback.h>
 #include <linux/netfs.h>
 
 #if defined(CONFIG_FSCACHE) || defined(CONFIG_FSCACHE_MODULE)
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index d1f65adf6a26..2fda288600d3 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -69,6 +69,7 @@ struct writeback_control {
 	unsigned for_reclaim:1;		/* Invoked from the page allocator */
 	unsigned range_cyclic:1;	/* range_start is cyclic */
 	unsigned for_sync:1;		/* sync(2) WB_SYNC_ALL writeback */
+	unsigned unpinned_fscache_wb:1;	/* Cleared I_PINNING_FSCACHE_WB */
 
 	/*
 	 * When writeback IOs are bounced through async layers, only the