On Tue, Sep 01, 2020 at 09:10:05AM +0800, Ming Lei wrote: > On Tue, Sep 1, 2020 at 8:53 AM Qian Cai <c...@lca.pw> wrote: > > > > On Fri, Aug 07, 2020 at 09:34:08PM +0900, Tetsuo Handa wrote: > > > On 2020/08/07 21:27, Al Viro wrote: > > > > On Fri, Aug 07, 2020 at 07:35:08PM +0900, Tetsuo Handa wrote: > > > >> syzbot is reporting hung task at pipe_release() [1], for > > > >> for_each_bvec() from > > > >> iterate_bvec() from iterate_all_kinds() from iov_iter_alignment() from > > > >> ext4_unaligned_io() from ext4_dio_write_iter() from > > > >> ext4_file_write_iter() from > > > >> call_write_iter() from do_iter_readv_writev() from do_iter_write() from > > > >> vfs_iter_write() from iter_file_splice_write() falls into infinite > > > >> busy loop > > > >> with pipe->mutex held. > > > >> > > > >> The reason of falling into infinite busy loop is that > > > >> iter_file_splice_write() > > > >> for some reason generates "struct bio_vec" entry with .bv_len=0 and > > > >> .bv_offset=0 > > > >> while for_each_bvec() cannot handle .bv_len == 0. > > > > > > > > broken in 1bdc76aea115 "iov_iter: use bvec iterator to implement > > > > iterate_bvec()", > > > > unless I'm misreading it... > > > > I have been chasing something similar for a while as in, > > > > https://lore.kernel.org/linux-fsdevel/89f418a9-eb20-48cb-9ae0-52c700e6b...@lca.pw/ > > > > In my case, it seems the endless loop happens in iterate_iovec() instead > > where > > I put a debug patch here, > > > > --- a/lib/iov_iter.c > > +++ b/lib/iov_iter.c > > @@ -33,6 +33,7 @@ > > if (unlikely(!__v.iov_len)) \ > > continue; \ > > __v.iov_base = __p->iov_base; \ > > + printk_ratelimited("ITER_IOVEC left = %zu, n = %zu\n", > > left, n); \ > > left = (STEP); \ > > __v.iov_len -= left; \ > > skip = __v.iov_len; \ > > > > and end up seeing overflows ("n" supposes to be less than PAGE_SIZE) before > > the > > soft-lockups and a dead system, > > > > [ 4300.249180][T470195] ITER_IOVEC left = 0, n = 48566423 > > > > Thoughts? > > Does the following patch make a difference for you? > > https://lore.kernel.org/linux-block/20200817100055.2495905-1-ming....@redhat.com/
Yes, it does. I could no longer be able to reproduce the soft lockups with the patch applied.
