On Tue, Jan 08, 2019 at 09:56:32AM -0700, Jens Axboe wrote: > For the upcoming async polled IO, we can't sleep allocating requests. > If we do, then we introduce a deadlock where the submitter already > has async polled IO in-flight, but can't wait for them to complete > since polled requests must be active found and reaped. > > Utilize the helper in the blockdev DIRECT_IO code. > > Signed-off-by: Jens Axboe <[email protected]> > --- > fs/block_dev.c | 4 ++-- > include/linux/bio.h | 14 ++++++++++++++ > 2 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/fs/block_dev.c b/fs/block_dev.c > index 5415579f3e14..2ebd2a0d7789 100644 > --- a/fs/block_dev.c > +++ b/fs/block_dev.c > @@ -233,7 +233,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct > iov_iter *iter, > task_io_account_write(ret); > } > if (iocb->ki_flags & IOCB_HIPRI) > - bio.bi_opf |= REQ_HIPRI; > + bio_set_polled(&bio, iocb); > > qc = submit_bio(&bio); > for (;;) { > @@ -401,7 +401,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter > *iter, int nr_pages) > nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES); > if (!nr_pages) { > if (iocb->ki_flags & IOCB_HIPRI) > - bio->bi_opf |= REQ_HIPRI; > + bio_set_polled(bio, iocb); > > qc = submit_bio(bio); > WRITE_ONCE(iocb->ki_cookie, qc); > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 7380b094dcca..f6f0a2b3cbc8 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio > *bio, struct page *page, > > #endif /* CONFIG_BLK_DEV_INTEGRITY */ > > +/* > + * Mark a bio as polled. Note that for async polled IO, the caller must > + * expect -EWOULDBLOCK if we cannot allocate a request (or other resources). > + * We cannot block waiting for requests on polled IO, as those completions > + * must be found by the caller. This is different than IRQ driven IO, where > + * it's safe to wait for IO to complete. > + */ > +static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb) > +{ > + bio->bi_opf |= REQ_HIPRI; > + if (!is_sync_kiocb(kiocb)) > + bio->bi_opf |= REQ_NOWAIT; > +} > +
REQ_NOWAIT doesn't cover allocating split bio, is that a issue? BTW, could you explain a bit about the deadlock in case of sleep from request allocation? Thanks, Ming
