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. :) thanks, -- John Hubbard NVIDIA
