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Subject[PATCH -next,v2 3/3] Revert "nfs: nfs_file_write() should check for writeback errors"
Date
This reverts commit ce368536dd614452407dc31e2449eb84681a06af.

Second `dd` of the following reproducer will be very very slow.
filemap_sample_wb_err() always return 0 if old wb error have not been consumed.
filemap_check_wb_err() will return the old error even if there is no new
writeback error between filemap_sample_wb_err() and filemap_check_wb_err().
Then nfs_need_check_write() always return true, nfs_wb_all() will be called
every time in nfs_file_write().

Reproducer:
nfs server | nfs client
-----------------------------|---------------------------------------------
# No space left on server |
fallocate -l 100G /svr/nospc |
| mount -t nfs $nfs_server_ip:/ /mnt
|
| # Expected error: No space left on device
| dd if=/dev/zero of=/mnt/file count=1 ibs=1M
|
| # Release space on mountpoint
| rm /mnt/nospc
|
| # very very slow
| dd if=/dev/zero of=/mnt/file count=1 ibs=1M

generic_perform_write() detect wb error by calling filemap_check_errors():
generic_perform_write
nfs_write_end
nfs_wb_all
filemap_write_and_wait
filemap_write_and_wait_range
filemap_check_errors

filemap_fdatawait_range() detect wb error by calling filemap_check_errors():
filemap_fdatawait_range
__filemap_fdatawait_range
filemap_check_errors

generic_write_sync() will also detect wb error by calling nfs_file_fsync():
generic_write_sync
vfs_fsync_range
nfs_file_fsync
file_write_and_wait_range
file_check_and_advance_wb_err
errseq_check_and_advance

When writeback error is detected in nfs_file_write(), we just goto label "out",
will not goto nfs_need_check_write(). So we remove the useless and problematic
checking.

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
---
fs/nfs/file.c | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 353f1f832519..49f1485a30bb 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -597,14 +597,12 @@ static const struct vm_operations_struct nfs_file_vm_ops = {
.page_mkwrite = nfs_vm_page_mkwrite,
};

-static int nfs_need_check_write(struct file *filp, struct inode *inode,
- int error)
+static int nfs_need_check_write(struct file *filp, struct inode *inode)
{
struct nfs_open_context *ctx;

ctx = nfs_file_open_context(filp);
- if (nfs_error_is_fatal_on_server(error) ||
- nfs_ctx_key_to_expire(ctx, inode))
+ if (nfs_ctx_key_to_expire(ctx, inode))
return 1;
return 0;
}
@@ -615,8 +613,6 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
struct inode *inode = file_inode(file);
unsigned int mntflags = NFS_SERVER(inode)->flags;
ssize_t result, written;
- errseq_t since;
- int error;

result = nfs_key_timeout_notify(file, inode);
if (result)
@@ -641,7 +637,6 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)

nfs_clear_invalid_mapping(file->f_mapping);

- since = filemap_sample_wb_err(file->f_mapping);
nfs_start_io_write(inode);
result = generic_write_checks(iocb, from);
if (result > 0) {
@@ -675,8 +670,7 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
goto out;

/* Return error values */
- error = filemap_check_wb_err(file->f_mapping, since);
- if (nfs_need_check_write(file, inode, error)) {
+ if (nfs_need_check_write(file, inode)) {
int err = nfs_wb_all(inode);
if (err < 0)
result = err;
--
2.31.1
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