Messages in this thread | | | From | Nikita Danilov <> | Date | Fri, 20 Sep 2002 20:32:55 +0400 | Subject | Re: locking rules for ->dirty_inode() |
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Andrew Morton writes: > Nikita Danilov wrote: > > > > Hello, > > > > Documentation/filesystems/Locking states that all super operations may > > block, but __set_page_dirty_buffers() calls > > > > __mark_inode_dirty()->s_op->dirty_inode() > > > > under mapping->private_lock spin lock. This seems strange, because file > > systems' ->dirty_inode() assume that they are allowed to block. For > > example, ext3_dirty_inode() allocates memory in > > > > ext3_journal_start()->journal_start()->new_handle()->... > > > > OK, thanks. > > mapping->private_lock is taken there to pin page->buffers() > (Can't lock the page because set_page_dirty is called under > page_table_lock, and other locks). > > I'm sure we can just move the spin_unlock up to above the > TestSetPageDirty(), but I need to zenuflect for a while over > why I did it that way. > > It's necessary to expose buffer-dirtiness and page-dirtiness > to the rest of the world in the correct order. If we set the > page dirty and then the buffers, there is a window in which writeback > could find the dirty page, try to write it, discover clean buffers > and mark the page clean. We would end up with a !PageDirty page, > on mapping->clean_pages, with dirty buffers. It would never be > written. > > Yup. We can move that spin_unlock up ten lines.
Actually, I came over this while trying to describe lock ordering in reiser4 after I just started integrating other kernel locks there. I wonder, has somebody already done this, writing up kernel lock hierarchy, that is?
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