On Mon, Jun 20, 2022 at 02:35:30PM +0800, Miaohe Lin wrote: > On 2022/6/20 12:47, Matthew Wilcox wrote: > > On Mon, Jun 20, 2022 at 09:56:06AM +0800, Miaohe Lin wrote: > >> On 2022/6/18 18:34, Matthew Wilcox wrote: > >>> On Sat, Jun 18, 2022 at 04:38:20PM +0800, Miaohe Lin wrote: > >>>> The invalidate_locks of two mappings should be unlocked in reverse order > >>>> relative to the locking order in filemap_invalidate_lock_two(). Modifying > >>> > >>> Why? It's perfectly valid to lock(A) lock(B) unlock(A) unlock(B). > >>> If it weren't we'd have lockdep check it and complain. > > It seems I misunderstand your word. I thought you said it must be at lock(A) lock(B) unlock(A) unlock(B) > order... Sorry. > > >> > >> For spin_lock, they are lock(A) lock(B) unlock(B) unlock(A) e.g. in copy_huge_pud, > > > > I think you need to spend some time thinking about the semantics of > > locks and try to figure out why it would make any difference at all > > which order locks (of any type) are _unlocked_ in, > > IIUC, the lock orders are important to prevent possible deadlock. But unlock orders should be relaxed > because they won't result in problem indeed. And what I advocate here is that making it at lock(A) lock(B) > unlock(B) unlock(A) order should be a better program practice. Or unlock order shouldn't be obligatory > at practice? > lock(A) lock(B) unlock(A) unlock(B) is fine. So it is better not to complicate the code. > Thanks. > > > > >> copy_huge_pmd, move_huge_pmd and so on: > >> dst_ptl = pmd_lock(dst_mm, dst_pmd); > >> src_ptl = pmd_lockptr(src_mm, src_pmd); > >> spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > >> ... > >> spin_unlock(src_ptl); > >> spin_unlock(dst_ptl); > >> > >> For rw_semaphore, they are also lock(A) lock(B) unlock(B) unlock(A) e.g. in dup_mmap(): > >> mmap_write_lock_killable(oldmm) > >> mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING); > >> ... > >> mmap_write_unlock(mm); > >> mmap_write_unlock(oldmm); > >> > >> and ntfs_extend_mft(): > >> down_write(&ni->file.run_lock); > >> down_write_nested(&sbi->used.bitmap.rw_lock, BITMAP_MUTEX_CLUSTERS); > >> ... > >> up_write(&sbi->used.bitmap.rw_lock); > >> up_write(&ni->file.run_lock); > >> > >> But I see some lock(A) lock(B) unlock(A) unlock(B) examples in some fs codes. Could you > >> please tell me the right lock/unlock order? I'm somewhat confused now... > >> > >> BTW: If lock(A) lock(B) unlock(A) unlock(B) is requested, filemap_invalidate_lock_two might > >> still need to be changed to respect that order? > >> > >> Thanks! > >> > >>> > >>> . > >>> > >> > > > > . > > > >
