On Tue, Sep 27, 2022 at 6:45 PM John Hubbard <jhubbard@xxxxxxxxxx> wrote: > > On 9/27/22 18:41, Huang, Ying wrote: > >>>> I also agree that we cannot make any rules such as "do not lock > 1 page > >>>> at the same time, elsewhere in the kernel", because it is already > >>>> happening, for example in page-writeback.c, which locks PAGEVEC_SIZE > >>>> (15) pages per batch [1]. > >> > >> That's not really the case though. The inner loop of write_cache_page() > >> only ever locks one page at a time, either directly via the > >> unlock_page() on L2338 (those goto's are amazing) or indirectly via > >> (*writepage)() on L2359. > >> > >> So there's no deadlock potential there because unlocking any previously > >> locked page(s) doesn't depend on obtaining the lock for another page. > >> Unless I've missed something? > > > > Yes. This is my understanding too after checking ext4_writepage(). > > > > Yes, I missed the ".writepage() shall unlock the page" design point. Now > it seems much more reasonable and safer. :) .writepage is deprecated (see https://lore.kernel.org/linux-fsdevel/20220719041311.709250-1-hch@xxxxxx/), write back actually uses .writepages. > > thanks, > > -- > John Hubbard > NVIDIA >
