On 2/9/21 12:51 AM, Christoph Hellwig wrote:
> On Mon, Feb 08, 2021 at 07:30:08PM -0700, Jens Axboe wrote:
>> + if (iocb->ki_flags & IOCB_NOWAIT) {
>> + if (filemap_range_needs_writeback(mapping, pos, end)) {
>> + ret = -EAGAIN;
>> + goto out_free_dio;
>> + }
>> + flags |= IOMAP_NOWAIT;
>> + }
>> if (iter_is_iovec(iter))
>> dio->flags |= IOMAP_DIO_DIRTY;
>> } else {
>> + if (iocb->ki_flags & IOCB_NOWAIT) {
>> + if (filemap_range_has_page(mapping, pos, end)) {
>> + ret = -EAGAIN;
>> + goto out_free_dio;
>> + }
>> + flags |= IOMAP_NOWAIT;
>> + }
>> +
>> flags |= IOMAP_WRITE;
>> dio->flags |= IOMAP_DIO_WRITE;
>>
>> @@ -478,14 +493,6 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>> dio->flags |= IOMAP_DIO_WRITE_FUA;
>> }
>>
>> - if (iocb->ki_flags & IOCB_NOWAIT) {
>> - if (filemap_range_has_page(mapping, pos, end)) {
>> - ret = -EAGAIN;
>> - goto out_free_dio;
>> - }
>> - flags |= IOMAP_NOWAIT;
>> - }
>
> looking at this I really hate the scheme with the potential racyness
> and duplicated page looksups.
Me too
> Why can't we pass a nonblock flag to filemap_write_and_wait_range
> and invalidate_inode_pages2_range that makes them return -EAGAIN
> when they would block to clean this whole mess up?
We could, but that's a _lot_ of surgery. I'd rather live with the
slight race for now instead of teaching writepages, page laundering,
etc about IOCB_NOWAIT.
I do think that's a worthy long term goal, but we dio read situation
is bad enough that it warrants a quicker fix.
--
Jens Axboe
