[PATCH 10/18] NFS: swap IO handling is slightly different for O_DIRECT IO
From: NeilBrown <hidden>
Date: 2021-12-16 23:53:33
Also in:
linux-nfs, lkml
Subsystem:
filesystems (vfs and infrastructure), nfs, sunrpc, and lockd clients, the rest · Maintainers:
Alexander Viro, Christian Brauner, Trond Myklebust, Anna Schumaker, Linus Torvalds
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 <redacted> --- fs/nfs/direct.c | 30 +++++++++++++++++++++--------- fs/nfs/file.c | 4 ++-- include/linux/nfs_fs.h | 4 ++-- 3 files changed, 25 insertions(+), 13 deletions(-)
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index f1e169f3050a..eeff1b4e1a7c 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c@@ -165,9 +165,9 @@ 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;
@@ -421,6 +421,7 @@ 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
@@ -436,7 +437,8 @@ 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;
@@ -478,12 +480,14 @@ 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);
@@ -872,6 +876,7 @@ 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
@@ -888,7 +893,8 @@ 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;
@@ -902,7 +908,11 @@ 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) + result = generic_write_checks(iocb, iter); + else + /* bypass generic checks */ + result = iov_iter_count(iter); if (result <= 0) return result; count = result;
@@ -933,7 +943,8 @@ 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) + nfs_start_io_direct(inode); requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);
@@ -942,7 +953,8 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) pos >> PAGE_SHIFT, end); } - nfs_end_io_direct(inode); + if (!swap) + 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 b620fe697158..996dfb3c74b2 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c@@ -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,
@@ -625,7 +625,7 @@ 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 6329e6958718..3a210478f665 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h@@ -512,9 +512,9 @@ static inline const struct cred *nfs_file_cred(struct file *file) */ extern int nfs_swap_rw(struct kiocb *, struct iov_iter *); extern ssize_t nfs_file_direct_read(struct kiocb *iocb, - struct iov_iter *iter); + struct iov_iter *iter, bool swap); extern ssize_t nfs_file_direct_write(struct kiocb *iocb, - struct iov_iter *iter); + struct iov_iter *iter, bool swap); /* * linux/fs/nfs/dir.c