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Message-ID: <164420916125.29374.6888726725038584805.stgit@noble.brown>
Date: Mon, 07 Feb 2022 15:46:01 +1100
From: NeilBrown <neilb@...e.de>
To: Trond Myklebust <trond.myklebust@...merspace.com>,
Anna Schumaker <anna.schumaker@...app.com>,
Chuck Lever <chuck.lever@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mark Hemment <markhemm@...glemail.com>,
Christoph Hellwig <hch@...radead.org>,
David Howells <dhowells@...hat.com>
Cc: linux-nfs@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 20/21] NFS: swap IO handling is slightly different for
O_DIRECT IO
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@...e.de>
---
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 b929dd5b0c3a..c5c53219beeb 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -166,9 +166,9 @@ int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE);
if (iov_iter_rw(iter) == READ)
- ret = nfs_file_direct_read(iocb, iter);
+ ret = nfs_file_direct_read(iocb, iter, true);
else
- ret = nfs_file_direct_write(iocb, iter);
+ ret = nfs_file_direct_write(iocb, iter, true);
if (ret < 0)
return ret;
return 0;
@@ -422,6 +422,7 @@ 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
@@ -437,7 +438,8 @@ 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;
@@ -479,12 +481,14 @@ 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);
@@ -873,6 +877,7 @@ 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
@@ -889,7 +894,8 @@ 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, requested;
size_t count;
@@ -903,7 +909,11 @@ 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;
@@ -934,16 +944,20 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
dreq->iocb = iocb;
pnfs_init_ds_commit_info_ops(&dreq->ds_cinfo, inode);
- 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 7d42117b210d..ceacae8e7a38 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -159,7 +159,7 @@ 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,
@@ -634,7 +634,7 @@ 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 58807406aff6..22aa5c08e3ed 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -507,10 +507,10 @@ static inline const struct cred *nfs_file_cred(struct file *file)
* linux/fs/nfs/direct.c
*/
int nfs_swap_rw(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
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