Hi Hin-Tak, On Tue, 2012-10-30 at 08:24 +0000, Hin-Tak Leung wrote: > [snip] > > > > Usually, hfs_bnode_read() is called after searching of some object in b-tree. > > It needs to initialize struct hfsplus_find_data by means of hfs_find_init() > > before any search and operations inside b-tree node. And then, it needs to > > call hfs_find_exit(). The hfsplus_find_data structure contains mutex that it > > locks of b-tree during hfs_find_init() call and unlock during > > hfs_find_exit(). And, usually, hfs_bnode_read() is placed > > between hfs_find_init()/hfs_find_exit() calls. So, as I can understand, your > > mutex inside hfs_bnode_read() is useless. But, maybe, not all hfs_bnode_read() > > calls are placed inside hfs_find_init()/hfs_find_exit() calls. It needs to check. > > > I can't clear understand about what simultaneous kmap()'s you are talking. > > As > > I can see, usually, (especially, in the case of hfs_bnode_read()) pairs of > > kmap()/kunmap() localize in small parts of code and I expect that it executes > > fast. Do I misunderstand something? > > Perhaps it is easier to show some code for the discussion. The attached > serializes kmap in hfs_bnode_read() . This makes the driver works more reliably, > somehow. In real usage, multiple instances of hfs_bnode_read() do get invoked in > parallel. I assume that is because of both SMP as well as file system access > itself are parallelized at various level - e.g. recursion like running du > probably invokes a few instances of readdir/getdents? > As I understand, readdir/getdents syscalls call hfsplus_readdir() method, as a result. It is called hfs_find_init() in the begin of hfsplus_readdir() (as in hfsplus_lookup() also). The hfs_find_init() method locks the mutex on the whole catalog tree. Then, it can be called hfs_bnode_read() and other methods that operates by b-tree content in the environment of locked b-tree. And, finally, it is called hfs_find_exit() method at the end of hfsplus_readdir(). The hfs_find_exit() method unlock the mutex. So, even if you have several threads with readdir/getdents calls then only one thread will operate with the b-tree inside hfsplus_readdir() operation. What serialized kmap in hfs_bnode_read() do you mean? How is it possible to have such situation for locked b-tree? > >> I tried swapping those by kmap_atomic()/kunmap_atomic() (beware the arguments are different for unmap) - but the kernel immediately warned that *_atom() code is used where code can sleep. > >> > > > > Could you describe in more details about warning? > > In hfs_bnode_read(), I tried changing kmap/kunmap to > kmap_atomic()/kunmap_atomic() . (Sorry I deleted the change since it does not > work - but it shouldn't be too difficult to redo since it is just changing two > lines in hfs_bnode_read()) - then I get many: > > BUG: scheduling while atomic: ... > It is strange. I need to check it. [snip] > BTW, I think I see another bug - unrelated to journalling - in the current hfs+ > code: folder counts are not updated correctly. It seems that hfs+ folders have > recursive folder counts (i.e. a parent dir knows how many sub-dir's it has, > without needing to recurse down), and this is currently not updated correctly. > One way of demo'ing this is to: > > (make sure fs is fsck-clean ; mount) > > cp -ipr somedir_with_some_files/ some_hfs+_place/someplace_inside/ > > (umount; run fsck_hfs again, now it complains about folder counts) > > The actual message looks a it like this: > > ** Checking catalog hierarchy. > HasFolderCount flag needs to be set (id = 393055) > (It should be 0x10 instead of 0) > Incorrect folder count in a directory (id = 205) > (It should be 18 instead of 17) Sorry, I can't reproduce this issue. I tried to reproduce as you described. Maybe, do you miss something? With the best regards, Vyacheslav Dubeyko. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
