[PATCH 13/23] fs: don't change the address limit for ->read_iter in __kernel_read

[Christoph Hellwig]

If we read to a file that implements ->read_iter there is no need
to change the address limit if we send a kvec down.

Signed-off-by: Christoph Hellwig <h...@lst.de>
---
 fs/read_write.c | 40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 6a2170eaee64f9..8bec4418543994 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -421,7 +421,6 @@ static ssize_t new_sync_read(struct file *filp, char __user 
*buf, size_t len, lo
 
 ssize_t __kernel_read(struct file *file, void *buf, size_t count, loff_t *pos)
 {
-       mm_segment_t old_fs = get_fs();
        ssize_t ret;
 
        if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))
@@ -431,14 +430,25 @@ ssize_t __kernel_read(struct file *file, void *buf, 
size_t count, loff_t *pos)
 
        if (count > MAX_RW_COUNT)
                count =  MAX_RW_COUNT;
-       set_fs(KERNEL_DS);
-       if (file->f_op->read)
+       if (file->f_op->read) {
+               mm_segment_t old_fs = get_fs();
+
+               set_fs(KERNEL_DS);
                ret = file->f_op->read(file, (void __user *)buf, count, pos);
-       else if (file->f_op->read_iter)
-               ret = new_sync_read(file, (void __user *)buf, count, pos);
-       else
+               set_fs(old_fs);
+       } else if (file->f_op->read_iter) {
+               struct kvec iov = { .iov_base = buf, .iov_len = count };
+               struct kiocb kiocb;
+               struct iov_iter iter;
+
+               init_sync_kiocb(&kiocb, file);
+               kiocb.ki_pos = *pos;
+               iov_iter_kvec(&iter, READ, &iov, 1, count);
+               ret = file->f_op->read_iter(&kiocb, &iter);
+               *pos = kiocb.ki_pos;
+       } else {
                ret = -EINVAL;
-       set_fs(old_fs);
+       }
        if (ret > 0) {
                fsnotify_access(file);
                add_rchar(current, ret);
@@ -520,7 +530,14 @@ ssize_t __kernel_write(struct file *file, const void *buf, 
size_t count,
 
        if (count > MAX_RW_COUNT)
                count =  MAX_RW_COUNT;
-       if (file->f_op->write_iter) {
+       if (file->f_op->write) {
+               mm_segment_t old_fs = get_fs();
+
+               set_fs(KERNEL_DS);
+               ret = file->f_op->write(file, (__force const char __user *)buf,
+                               count, pos);
+               set_fs(old_fs);
+       } else if (file->f_op->write_iter) {
                struct kvec iov = { .iov_base = (void *)buf, .iov_len = count };
                struct kiocb kiocb;
                struct iov_iter iter;
@@ -531,13 +548,6 @@ ssize_t __kernel_write(struct file *file, const void *buf, 
size_t count,
                ret = file->f_op->write_iter(&kiocb, &iter);
                if (ret > 0)
                        *pos = kiocb.ki_pos;
-       } else if (file->f_op->write) {
-               mm_segment_t old_fs = get_fs();
-
-               set_fs(KERNEL_DS);
-               ret = file->f_op->write(file, (__force const char __user *)buf,
-                               count, pos);
-               set_fs(old_fs);
        } else {
                ret = -EINVAL;
        }
-- 
2.26.2