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* [PATCH 1/3] afs: Handle len being extending over page end in write_begin/write_end
@ 2021-06-14 13:20 David Howells
  2021-06-14 13:20 ` [PATCH 2/3] afs: Fix afs_write_end() to handle short writes David Howells
                   ` (3 more replies)
  0 siblings, 4 replies; 15+ messages in thread
From: David Howells @ 2021-06-14 13:20 UTC (permalink / raw)
  To: jlayton, willy
  Cc: linux-afs, dhowells, linux-afs, ceph-devel, linux-fsdevel, linux-kernel

With transparent huge pages, in the future, write_begin() and write_end()
may be passed a length parameter that, in combination with the offset into
the page, exceeds the length of that page.  This allows
grab_cache_page_write_begin() to better choose the size of THP to allocate.

Fix afs's functions to handle this by trimming the length as needed after
the page has been allocated.

Fixes: e1b1240c1ff5 ("netfs: Add write_begin helper")
Reported-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-afs@lists.infradead.org
---

 fs/afs/write.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index a523bb86915d..f68274c39f47 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -25,7 +25,8 @@ int afs_set_page_dirty(struct page *page)
 }
 
 /*
- * prepare to perform part of a write to a page
+ * Prepare to perform part of a write to a page.  Note that len may extend
+ * beyond the end of the page.
  */
 int afs_write_begin(struct file *file, struct address_space *mapping,
 		    loff_t pos, unsigned len, unsigned flags,
@@ -52,7 +53,8 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
 		return ret;
 
 	index = page->index;
-	from = pos - index * PAGE_SIZE;
+	from = offset_in_thp(page, pos);
+	len = min_t(size_t, len, thp_size(page) - from);
 	to = from + len;
 
 try_again:
@@ -103,7 +105,8 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
 }
 
 /*
- * finalise part of a write to a page
+ * Finalise part of a write to a page.  Note that len may extend beyond the end
+ * of the page.
  */
 int afs_write_end(struct file *file, struct address_space *mapping,
 		  loff_t pos, unsigned len, unsigned copied,
@@ -111,7 +114,7 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 {
 	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 	unsigned long priv;
-	unsigned int f, from = pos & (thp_size(page) - 1);
+	unsigned int f, from = offset_in_thp(page, pos);
 	unsigned int t, to = from + copied;
 	loff_t i_size, maybe_i_size;
 



^ permalink raw reply	[flat|nested] 15+ messages in thread

end of thread, other threads:[~2021-06-18  3:40 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-06-14 13:20 [PATCH 1/3] afs: Handle len being extending over page end in write_begin/write_end David Howells
2021-06-14 13:20 ` [PATCH 2/3] afs: Fix afs_write_end() to handle short writes David Howells
2021-06-14 13:28   ` Matthew Wilcox
2021-06-14 13:37   ` David Howells
2021-06-14 13:46     ` Matthew Wilcox
2021-06-18  3:40       ` Al Viro
2021-06-14 14:04     ` David Howells
2021-06-14 14:37   ` Matthew Wilcox
2021-06-14 15:38   ` David Howells
2021-06-14 15:43     ` Matthew Wilcox
2021-06-14 21:11     ` David Howells
2021-06-14 13:20 ` [PATCH 3/3] netfs: fix test for whether we can skip read when writing beyond EOF David Howells
2021-06-15 17:01   ` Jeff Layton
2021-06-14 13:33 ` David Howells
2021-06-17  7:43 ` [PATCH 1/3] afs: Handle len being extending over page end in write_begin/write_end kernel test robot

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