[PATCH 4.19 294/338] NFS: swap IO handling is slightly different for O_DIRECT IO

Greg Kroah-Hartman
2022-04-14T14:11:11Z

From: NeilBrown <neilb@suse.de>

[ Upstream commit 64158668ac8b31626a8ce48db4cad08496eb8340 ]

1/ Taking the i_rwsem for swap IO triggers lockdep warnings regarding
possible deadlocks with "fs_reclaim". These deadlocks could, I believe,
eventuate if a buffered read on the swapfile was attempted.

We don't need coherence with the page cache for a swap file, and
buffered writes are forbidden anyway. There is no other need for
i_rwsem during direct IO. So never take it for swap_rw()

2/ generic_write_checks() explicitly forbids writes to swap, and
performs checks that are not needed for swap. So bypass it
for swap_rw().

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/nfs/direct.c | 42 ++++++++++++++++++++++++++++--------------
fs/nfs/file.c | 4 ++--
include/linux/nfs_fs.h | 8 ++++----
3 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index e5da9d7fb69e..41ff316cd6ad 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -288,8 +288,8 @@ ssize_t nfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE);

if (iov_iter_rw(iter) == READ)
- return nfs_file_direct_read(iocb, iter);
- return nfs_file_direct_write(iocb, iter);
+ return nfs_file_direct_read(iocb, iter, true);
+ return nfs_file_direct_write(iocb, iter, true);
}

static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
@@ -553,6 +553,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
* nfs_file_direct_read - file direct read operation for NFS files
* @iocb: target I/O control block
* @iter: vector of user buffers into which to read data
+ * @swap: flag indicating this is swap IO, not O_DIRECT IO
*
* We use this function for direct reads instead of calling
* generic_file_aio_read() in order to avoid gfar's check to see if
@@ -568,7 +569,8 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
* client must read the updated atime from the server back into its
* cache.
*/
-ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter)
+ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter,
+ bool swap)
{
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
@@ -610,12 +612,14 @@ ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter)
if (iter_is_iovec(iter))
dreq->flags = NFS_ODIRECT_SHOULD_DIRTY;

- nfs_start_io_direct(inode);
+ if (!swap)
+ nfs_start_io_direct(inode);

NFS_I(inode)->read_io += count;
requested = nfs_direct_read_schedule_iovec(dreq, iter, iocb->ki_pos);

- nfs_end_io_direct(inode);
+ if (!swap)
+ nfs_end_io_direct(inode);

if (requested > 0) {
result = nfs_direct_wait(dreq);
@@ -971,6 +975,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
* nfs_file_direct_write - file direct write operation for NFS files
* @iocb: target I/O control block
* @iter: vector of user buffers from which to write data
+ * @swap: flag indicating this is swap IO, not O_DIRECT IO
*
* We use this function for direct writes instead of calling
* generic_file_aio_write() in order to avoid taking the inode
@@ -987,7 +992,8 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
* Note that O_APPEND is not supported for NFS direct writes, as there
* is no atomic O_APPEND write facility in the NFS protocol.
*/
-ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
+ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter,
+ bool swap)
{
ssize_t result = -EINVAL, requested;
size_t count;
@@ -1001,7 +1007,11 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
dfprintk(FILE, "NFS: direct write(%pD2, %zd@%Ld)\n",
file, iov_iter_count(iter), (long long) iocb->ki_pos);

- result = generic_write_checks(iocb, iter);
+ if (swap)
+ /* bypass generic checks */
+ result = iov_iter_count(iter);
+ else
+ result = generic_write_checks(iocb, iter);
if (result <= 0)
return result;
count = result;
@@ -1031,16 +1041,20 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
if (!is_sync_kiocb(iocb))
dreq->iocb = iocb;

- nfs_start_io_direct(inode);
+ if (swap) {
+ requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);
+ } else {
+ nfs_start_io_direct(inode);

- requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);
+ requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);

- if (mapping->nrpages) {
- invalidate_inode_pages2_range(mapping,
- pos >> PAGE_SHIFT, end);
- }
+ if (mapping->nrpages) {
+ invalidate_inode_pages2_range(mapping,
+ pos >> PAGE_SHIFT, end);
+ }

- nfs_end_io_direct(inode);
+ nfs_end_io_direct(inode);
+ }

if (requested > 0) {
result = nfs_direct_wait(dreq);
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 29553fdba8af..62a86c414391 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -157,7 +157,7 @@ nfs_file_read(struct kiocb *iocb, struct iov_iter *to)
ssize_t result;

if (iocb->ki_flags & IOCB_DIRECT)
- return nfs_file_direct_read(iocb, to);
+ return nfs_file_direct_read(iocb, to, false);

dprintk("NFS: read(%pD2, %zu@%lu)\n",
iocb->ki_filp,
@@ -606,7 +606,7 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
return result;

if (iocb->ki_flags & IOCB_DIRECT)
- return nfs_file_direct_write(iocb, from);
+ return nfs_file_direct_write(iocb, from, false);

dprintk("NFS: write(%pD2, %zu@%Ld)\n",
file, iov_iter_count(from), (long long) iocb->ki_pos);
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 0ff7dd2bf8a4..8ea7ceed8285 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -475,10 +475,10 @@ static inline struct rpc_cred *nfs_file_cred(struct file *file)
* linux/fs/nfs/direct.c
*/
extern ssize_t nfs_direct_IO(struct kiocb *, struct iov_iter *);
-extern ssize_t nfs_file_direct_read(struct kiocb *iocb,
- struct iov_iter *iter);
-extern ssize_t nfs_file_direct_write(struct kiocb *iocb,
- struct iov_iter *iter);
+ssize_t nfs_file_direct_read(struct kiocb *iocb,
+ struct iov_iter *iter, bool swap);
+ssize_t nfs_file_direct_write(struct kiocb *iocb,
+ struct iov_iter *iter, bool swap);

/*
* linux/fs/nfs/dir.c
--
2.35.1