mm/filemap: don't revert iter on -EIOCBQUEUED

Currently, if I/O is enqueued for async execution direct paths of
generic_file_{read,write}_iter() will always revert the iter.  There are
no users expecting that, and that is also costly.  Leave iterators as is
on -EIOCBQUEUED.

Link: https://lkml.kernel.org/r/f5247b60e7abbd2ff850cd108491f53a2e0c501a.1610207781.git.asml.silence@gmail.com
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 7dfed3454a2e10311c89b470f7ae46a56ba7f3ff..774a869da10681387956de311c56f60bfef60bd9 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2615,7 +2615,8 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
                        iocb->ki_pos += retval;
                        count -= retval;
                }
-               iov_iter_revert(iter, count - iov_iter_count(iter));
+               if (retval != -EIOCBQUEUED)
+                       iov_iter_revert(iter, count - iov_iter_count(iter));
 
                /*
                 * Btrfs can have a short DIO read if we encounter
@@ -3426,7 +3427,8 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
                }
                iocb->ki_pos = pos;
        }
-       iov_iter_revert(from, write_len - iov_iter_count(from));
+       if (written != -EIOCBQUEUED)
+               iov_iter_revert(from, write_len - iov_iter_count(from));
 out:
        return written;
 }