[05/11] afs: Fix to take ref on page when PG_private is set

Commit Message

David Howells Oct. 28, 2020, 2:10 p.m. UTC

Fix afs to take a ref on a page when it sets PG_private on it and to drop
the ref when removing the flag.

Note that in afs_write_begin(), a lot of the time, PG_private is already
set on a page to which we're going to add some data.  In such a case, we
leave the bit set and mustn't increment the page count.  To this end, make
TestSetPagePrivate() available.

Fixes: 31143d5d515e ("AFS: implement basic file write support")
Reported-by: Matthew Wilcox (Oracle) <[e-mail]>
Signed-off-by: David Howells <[e-mail]>
---

 fs/afs/dir.c               |    3 +++
 fs/afs/dir_edit.c          |    1 +
 fs/afs/file.c              |    2 ++
 fs/afs/write.c             |    9 +++++++--
 include/linux/page-flags.h |    1 +
 5 files changed, 14 insertions(+), 2 deletions(-)

Comments

David Howells Oct. 28, 2020, 3:24 p.m. UTC | #1

Matthew Wilcox <[e-mail]> wrote:

> There's an efficiency question here that I can't answer ... how often do
> you call afs_write_begin() on a page which already has PagePrivate set?

That's a question only userspace can answer - but think shell scripts that do
lots of small appends.

David

Patch

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 1d2e61e0ab04..064eb66c33e9 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -283,6 +283,7 @@  static struct afs_read *afs_read_dir(struct afs_vnode *dvnode, struct key *key)
 
 			set_page_private(req->pages[i], 1);
 			SetPagePrivate(req->pages[i]);
+			get_page(req->pages[i]);
 			unlock_page(req->pages[i]);
 			i++;
 		} else {
@@ -1977,6 +1978,7 @@  static int afs_dir_releasepage(struct page *page, gfp_t gfp_flags)
 
 	set_page_private(page, 0);
 	ClearPagePrivate(page);
+	put_page(page);
 
 	/* The directory will need reloading. */
 	if (test_and_clear_bit(AFS_VNODE_DIR_VALID, &dvnode->flags))
@@ -2006,5 +2008,6 @@  static void afs_dir_invalidatepage(struct page *page, unsigned int offset,
 	if (offset == 0 && length == PAGE_SIZE) {
 		set_page_private(page, 0);
 		ClearPagePrivate(page);
+		put_page(page);
 	}
 }
diff --git a/fs/afs/dir_edit.c b/fs/afs/dir_edit.c
index b108528bf010..997f6798beee 100644
--- a/fs/afs/dir_edit.c
+++ b/fs/afs/dir_edit.c
@@ -246,6 +246,7 @@  void afs_edit_dir_add(struct afs_vnode *vnode,
 			if (!PagePrivate(page)) {
 				set_page_private(page, 1);
 				SetPagePrivate(page);
+				get_page(page);
 			}
 			dir_page = kmap(page);
 		}
diff --git a/fs/afs/file.c b/fs/afs/file.c
index 91225421ad37..7dafa2266048 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -632,6 +632,7 @@  static void afs_invalidatepage(struct page *page, unsigned int offset,
 					     page->index, priv);
 			set_page_private(page, 0);
 			ClearPagePrivate(page);
+			put_page(page);
 		}
 	}
 
@@ -666,6 +667,7 @@  static int afs_releasepage(struct page *page, gfp_t gfp_flags)
 				     page->index, priv);
 		set_page_private(page, 0);
 		ClearPagePrivate(page);
+		put_page(page);
 	}
 
 	/* indicate that the page can be released */
diff --git a/fs/afs/write.c b/fs/afs/write.c
index b937ec047ec9..29685947324e 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -151,7 +151,8 @@  int afs_write_begin(struct file *file, struct address_space *mapping,
 	priv |= f;
 	trace_afs_page_dirty(vnode, tracepoint_string("begin"),
 			     page->index, priv);
-	SetPagePrivate(page);
+	if (!TestSetPagePrivate(page))
+		get_page(page);
 	set_page_private(page, priv);
 	_leave(" = 0");
 	return 0;
@@ -338,6 +339,8 @@  static void afs_pages_written_back(struct afs_vnode *vnode,
 			trace_afs_page_dirty(vnode, tracepoint_string("clear"),
 					     pv.pages[loop]->index, priv);
 			set_page_private(pv.pages[loop], 0);
+			ClearPagePrivate(pv.pages[loop]);
+			put_page(pv.pages[loop]);
 			end_page_writeback(pv.pages[loop]);
 		}
 		first += count;
@@ -863,7 +866,8 @@  vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	priv |= 0; /* From */
 	trace_afs_page_dirty(vnode, tracepoint_string("mkwrite"),
 			     vmf->page->index, priv);
-	SetPagePrivate(vmf->page);
+	if (!TestSetPagePrivate(vmf->page))
+		get_page(vmf->page);
 	set_page_private(vmf->page, priv);
 	file_update_time(file);
 
@@ -930,6 +934,7 @@  int afs_launder_page(struct page *page)
 			     page->index, priv);
 	set_page_private(page, 0);
 	ClearPagePrivate(page);
+	put_page(page);
 
 #ifdef CONFIG_AFS_FSCACHE
 	if (PageFsCache(page)) {
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 4f6ba9379112..37d65b55a6c6 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -365,6 +365,7 @@  PAGEFLAG(SwapBacked, swapbacked, PF_NO_TAIL)
  */
 PAGEFLAG(Private, private, PF_ANY) __SETPAGEFLAG(Private, private, PF_ANY)
 	__CLEARPAGEFLAG(Private, private, PF_ANY)
+	TESTSETFLAG(Private, private, PF_ANY)
 PAGEFLAG(Private2, private_2, PF_ANY) TESTSCFLAG(Private2, private_2, PF_ANY)
 PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY)
 	TESTCLEARFLAG(OwnerPriv1, owner_priv_1, PF_ANY)