Re: [RFC PATCH v2 1/5] nfs: Fix write to swapfile failure due to generic_write_checks()

Matthew Wilcox
2021-08-13T03:10:44Z

On Thu, Aug 12, 2021 at 09:22:06PM +0100, David Howells wrote:
> Trying to use a swapfile on NFS results in every DIO write failing with
> ETXTBSY because generic_write_checks(), as called by nfs_direct_write()
> from nfs_direct_IO(), forbids writes to swapfiles.

Why does nfs_direct_write() call generic_write_checks()?

ie call generic_write_checks() earlier, and only swap would bypass them.

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 2e894fec036b..7e2ca6b5fc5f 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -905,9 +905,6 @@ 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 (result <= 0)
- return result;
count = result;
nfs_add_stats(mapping->host, NFSIOS_DIRECTWRITTENBYTES, count);

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 1fef107961bc..91b2e3214836 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -611,6 +611,10 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
errseq_t since;
int error;

+ result = generic_write_checks(iocb, from);
+ if (result < 0)
+ return result;
+
result = nfs_key_timeout_notify(file, inode);
if (result)
return result;
@@ -621,8 +625,6 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
dprintk("NFS: write(%pD2, %zu@%Ld)\n",
file, iov_iter_count(from), (long long) iocb->ki_pos);

- if (IS_SWAPFILE(inode))
- goto out_swapfile;
/*
* O_APPEND implies that we must revalidate the file length.
*/
@@ -636,7 +638,6 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)

since = filemap_sample_wb_err(file->f_mapping);
nfs_start_io_write(inode);
- result = generic_write_checks(iocb, from);
if (result > 0) {
current->backing_dev_info = inode_to_bdi(inode);
result = generic_perform_write(file, from, iocb->ki_pos);
@@ -677,10 +678,6 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
nfs_add_stats(inode, NFSIOS_NORMALWRITTENBYTES, written);
out:
return result;
-
-out_swapfile:
- printk(KERN_INFO "NFS: attempt to write to active swap file!\n");
- return -ETXTBSY;
}
EXPORT_SYMBOL_GPL(nfs_file_write);