On Sat, Nov 22, 2008 at 03:46:25PM -0500, Theodore Tso wrote: > On Fri, Nov 21, 2008 at 10:10:46PM +0530, Aneesh Kumar K.V wrote: > > Indicate that the group locks can be taken in loop. > > I've been looking at this patch more closely, and I think there's a > major problem here. OK, after looking at this in yet more detail (and having changed planes in Dallas :-), I am more than ever convinced this patch is not rightq. We have an rw_sem for each block group, grp->alloc_sem, which is allocated in groups of meta blockgroups. The whole reason why we should worry about keeping them in the same class is we should worry about is if for some reason, the multiblock allocator happens to allocate two block group's alloc_sem, but one does them out of order (say, bg 4, then bg 2, while another does bg 2, then 4), we would get a dead lock. I'm guessing that what caused the problem for you was ext4_mb_init_group(), which if you are using 1k filesystems, tries to grab multiple grp->alloc_sem's. In each place where we find those, we need to use down_write_nested --- see Documentation/lockdep-design.txt. If there are any other places in mballoc.c which grabs multiple alloc_sem's at the same time, we'll have to use define new subclasses. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
