[PATCH 10/10] afs: Fix afs_invalidatepage to adjust the dirty region

[David Howells]

Fix afs_invalidatepage() to adjust the dirty region recorded in
page->private when truncating a page.  If the dirty region is entirely
removed, then the private data is cleared and the page dirty state is
cleared.

Without this, if the page is truncated and then expanded again by truncate,
zeros from the expanded, but no-longer dirty region may get written back to
the server if the page gets laundered due to a conflicting 3rd-party write.

It mustn't, however, shorten the dirty region of the page if that page is
still mmapped and has been marked dirty by afs_page_mkwrite(), so a flag is
stored in page->private to record this.

Fixes: 4343d00872e1 ("afs: Get rid of the afs_writeback record")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 fs/afs/file.c              |   74 +++++++++++++++++++++++++++++++++++++-------
 fs/afs/internal.h          |   16 ++++++++--
 fs/afs/write.c             |    1 +
 include/trace/events/afs.h |    5 ++-
 4 files changed, 80 insertions(+), 16 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 7dafa2266048..e3cec86cc6ef 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -601,6 +601,65 @@ static int afs_readpages(struct file *file, struct address_space *mapping,
 	return ret;
 }
 
+/*
+ * Adjust the dirty region of the page on truncation or full invalidation,
+ * getting rid of the markers altogether if the region is entirely invalidated.
+ */
+static void afs_invalidate_dirty(struct page *page, unsigned int offset,
+				 unsigned int length)
+{
+	struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
+	unsigned long priv;
+	unsigned int f, t, end = offset + length;
+
+	priv = page_private(page);
+
+	/* we clean up only if the entire page is being invalidated */
+	if (offset == 0 && length == thp_size(page))
+		goto full_invalidate;
+
+	 /* If the page was dirtied by page_mkwrite(), the PTE stays writable
+	  * and we don't get another notification to tell us to expand it
+	  * again.
+	  */
+	if (afs_is_page_dirty_mmapped(priv))
+		return;
+
+	/* We may need to shorten the dirty region */
+	f = afs_page_dirty_from(priv);
+	t = afs_page_dirty_to(priv);
+
+	if (t <= offset || f >= end)
+		return; /* Doesn't overlap */
+
+	if (f < offset && t > end)
+		return; /* Splits the dirty region - just absorb it */
+
+	if (f >= offset && t <= end)
+		goto undirty;
+
+	if (f < offset)
+		t = offset;
+	else
+		f = end;
+	if (f == t)
+		goto undirty;
+
+	priv = afs_page_dirty(f, t);
+	set_page_private(page, priv);
+	trace_afs_page_dirty(vnode, tracepoint_string("trunc"), page->index, priv);
+	return;
+
+undirty:
+	trace_afs_page_dirty(vnode, tracepoint_string("undirty"), page->index, priv);
+	clear_page_dirty_for_io(page);
+full_invalidate:
+	trace_afs_page_dirty(vnode, tracepoint_string("inval"), page->index, priv);
+	set_page_private(page, 0);
+	ClearPagePrivate(page);
+	put_page(page);
+}
+
 /*
  * invalidate part or all of a page
  * - release a page and clean up its private data if offset is 0 (indicating
@@ -609,9 +668,6 @@ static int afs_readpages(struct file *file, struct address_space *mapping,
 static void afs_invalidatepage(struct page *page, unsigned int offset,
 			       unsigned int length)
 {
-	struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
-	unsigned long priv;
-
 	_enter("{%lu},%u,%u", page->index, offset, length);
 
 	BUG_ON(!PageLocked(page));
@@ -625,17 +681,11 @@ static void afs_invalidatepage(struct page *page, unsigned int offset,
 			fscache_uncache_page(vnode->cache, page);
 		}
 #endif
-
-		if (PagePrivate(page)) {
-			priv = page_private(page);
-			trace_afs_page_dirty(vnode, tracepoint_string("inval"),
-					     page->index, priv);
-			set_page_private(page, 0);
-			ClearPagePrivate(page);
-			put_page(page);
-		}
 	}
 
+	if (PagePrivate(page))
+		afs_invalidate_dirty(page, offset, length);
+
 	_leave("");
 }
 
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 0ff1088a7c87..bf8fb9863b0e 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -864,11 +864,13 @@ struct afs_vnode_cache_aux {
  * 0...PAGE_SIZE inclusive, so we can't support 64K pages on a 32-bit system.
  */
 #if PAGE_SIZE > 32768
-#define __AFS_PAGE_PRIV_MASK	0xffffffff
+#define __AFS_PAGE_PRIV_MASK	0x7fffffff
 #define __AFS_PAGE_PRIV_SHIFT	32
+#define __AFS_PRIV_MMAPPED	0x80000000
 #else
-#define __AFS_PAGE_PRIV_MASK	0xffff
+#define __AFS_PAGE_PRIV_MASK	0x7fff
 #define __AFS_PAGE_PRIV_SHIFT	16
+#define __AFS_PRIV_MMAPPED	0x8000
 #endif
 
 static inline unsigned int afs_page_dirty_from(unsigned long priv)
@@ -886,6 +888,16 @@ static inline unsigned long afs_page_dirty(unsigned int from, unsigned int to)
 	return ((unsigned long)(to - 1) << __AFS_PAGE_PRIV_SHIFT) | from;
 }
 
+static inline unsigned long afs_page_dirty_mmapped(unsigned long priv)
+{
+	return priv | __AFS_PRIV_MMAPPED;
+}
+
+static inline bool afs_is_page_dirty_mmapped(unsigned long priv)
+{
+	return priv & __AFS_PRIV_MMAPPED;
+}
+
 #include <trace/events/afs.h>
 
 /*****************************************************************************/
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 91bc2cb2cad1..057d02fd4d02 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -871,6 +871,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	wait_on_page_writeback(vmf->page);
 
 	priv = afs_page_dirty(0, PAGE_SIZE);
+	priv = afs_page_dirty_mmapped(priv);
 	trace_afs_page_dirty(vnode, tracepoint_string("mkwrite"),
 			     vmf->page->index, priv);
 	if (!TestSetPagePrivate(vmf->page))
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index e718ae17ad91..91d515cb3aed 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -986,10 +986,11 @@ TRACE_EVENT(afs_page_dirty,
 		    __entry->priv = priv;
 			   ),
 
-	    TP_printk("vn=%p %lx %s %x-%x",
+	    TP_printk("vn=%p %lx %s %x-%x%s",
 		      __entry->vnode, __entry->page, __entry->where,
 		      afs_page_dirty_from(__entry->priv),
-		      afs_page_dirty_to(__entry->priv))
+		      afs_page_dirty_to(__entry->priv),
+		      afs_is_page_dirty_mmapped(__entry->priv) ? " M" : "")
 	    );
 
 TRACE_EVENT(afs_call_state,