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

David Howells
2021-10-18T14:51:32Z

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@redhat.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