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Commit 66cf5de0 authored by NeilBrown's avatar NeilBrown Committed by Greg Kroah-Hartman
Browse files

NFS: swap IO handling is slightly different for O_DIRECT IO 



[ 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: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent fa47286c

fs/nfs/direct.c

+28 −14
Original line number Diff line number Diff line
@@ -272,8 +272,8 @@ 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)
@@ -524,6 +524,7 @@ 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
@@ -539,7 +540,8 @@ 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;
@@ -581,11 +583,13 @@ ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter) 
	if (iter_is_iovec(iter))

		dreq->flags = NFS_ODIRECT_SHOULD_DIRTY;



	if (!swap)

		nfs_start_io_direct(inode);



	NFS_I(inode)->read_io += count;

	requested = nfs_direct_read_schedule_iovec(dreq, iter, iocb->ki_pos);



	if (!swap)

		nfs_end_io_direct(inode);



	if (requested > 0) {
@@ -937,6 +941,7 @@ 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
@@ -953,7 +958,8 @@ 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;
@@ -967,6 +973,10 @@ 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);



	if (swap)

		/* bypass generic checks */

		result =  iov_iter_count(iter);

	else

		result = generic_write_checks(iocb, iter);

	if (result <= 0)

		return result;
@@ -997,6 +1007,9 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) 
	if (!is_sync_kiocb(iocb))

		dreq->iocb = iocb;



	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);
@@ -1007,6 +1020,7 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) 
		}



		nfs_end_io_direct(inode);

	}



	if (requested > 0) {

		result = nfs_direct_wait(dreq);

fs/nfs/file.c

+2 −2
Original line number Diff line number Diff line
@@ -161,7 +161,7 @@ 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,
@@ -609,7 +609,7 @@ 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);

include/linux/nfs_fs.h

+4 −4
Original line number Diff line number Diff line
@@ -480,10 +480,10 @@ static inline const struct 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