This is a note to let you know that I've just added the patch titled
dax: Avoid page invalidation races and unnecessary radix tree traversals
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dax-avoid-page-invalidation-races-and-unnecessary-radix-tree-traversals.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Wed Dec 6 17:39:55 CET 2017
From: Jan Kara <jack@xxxxxxx>
Date: Wed, 10 Aug 2016 17:10:28 +0200
Subject: dax: Avoid page invalidation races and unnecessary radix tree traversals
From: Jan Kara <jack@xxxxxxx>
[ Upstream commit e3fce68cdbed297d927e993b3ea7b8b1cee545da ]
Currently dax_iomap_rw() takes care of invalidating page tables and
evicting hole pages from the radix tree when write(2) to the file
happens. This invalidation is only necessary when there is some block
allocation resulting from write(2). Furthermore in current place the
invalidation is racy wrt page fault instantiating a hole page just after
we have invalidated it.
So perform the page invalidation inside dax_iomap_actor() where we can
do it only when really necessary and after blocks have been allocated so
nobody will be instantiating new hole pages anymore.
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 28 +++++++++++-----------------
1 file changed, 11 insertions(+), 17 deletions(-)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1265,6 +1265,17 @@ iomap_dax_actor(struct inode *inode, lof
if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
return -EIO;
+ /*
+ * Write can allocate block for an area which has a hole page mapped
+ * into page tables. We have to tear down these mappings so that data
+ * written by write(2) is visible in mmap.
+ */
+ if ((iomap->flags & IOMAP_F_NEW) && inode->i_mapping->nrpages) {
+ invalidate_inode_pages2_range(inode->i_mapping,
+ pos >> PAGE_SHIFT,
+ (end - 1) >> PAGE_SHIFT);
+ }
+
while (pos < end) {
unsigned offset = pos & (PAGE_SIZE - 1);
struct blk_dax_ctl dax = { 0 };
@@ -1329,23 +1340,6 @@ iomap_dax_rw(struct kiocb *iocb, struct
if (iov_iter_rw(iter) == WRITE)
flags |= IOMAP_WRITE;
- /*
- * Yes, even DAX files can have page cache attached to them: A zeroed
- * page is inserted into the pagecache when we have to serve a write
- * fault on a hole. It should never be dirtied and can simply be
- * dropped from the pagecache once we get real data for the page.
- *
- * XXX: This is racy against mmap, and there's nothing we can do about
- * it. We'll eventually need to shift this down even further so that
- * we can check if we allocated blocks over a hole first.
- */
- if (mapping->nrpages) {
- ret = invalidate_inode_pages2_range(mapping,
- pos >> PAGE_SHIFT,
- (pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT);
- WARN_ON_ONCE(ret);
- }
-
while (iov_iter_count(iter)) {
ret = iomap_apply(inode, pos, iov_iter_count(iter), flags, ops,
iter, iomap_dax_actor);
Patches currently in stable-queue which might be from jack@xxxxxxx are
queue-4.9/mm-avoid-returning-vm_fault_retry-from-page_mkwrite-handlers.patch
queue-4.9/dax-avoid-page-invalidation-races-and-unnecessary-radix-tree-traversals.patch