On Thu, 8 Mar 2012 15:19:27 -0600 Tyler Hicks <tyhicks@xxxxxxxxxxxxx> wrote: > > > > > > Sigh. Was lockdep_annotate_inode_mutex_key() sufficiently > > self-explanatory to justify leaving it undocumented? > > > > <goes off and reads e096d0c7e2e> > > > > OK, the patch looks correct given the explanation in e096d0c7e2e, but > > I'd like to understand why it becomes necessary only now. > > > > > NOTE: This patch also require > > > http://thread.gmane.org/gmane.linux.file-systems/58795/focus=59565 > > > to remove the lockdep warning > > > > And that patch has been basically ignored. > > Al commented on it here: > > https://lkml.org/lkml/2012/2/16/518 > > He said that while my patch is correct, taking i_mutex inside mmap_sem > is still wrong. OK, thanks, yup. Taking i_mutex in file_operations.mmap() is wrong. Is hugetlbfs actually deadlockable because of this, or is it the case that the i_mutex->mmap_sem ordering happens to never happen for this filesystem? Although we shouldn't go and create incompatible lock ranking rules for different filesystems! So we need to pull the i_mutex out of hugetlbfs_file_mmap(). What's it actually trying to do in there? If we switch to i_size_read()/i_size_write() then AFAICT the problem comes down to hugetlb_reserve_pages(). hugetlb_reserve_pages() fiddles with i_mapping->private_list and the fs owns private_list and is free to use a lock other than i_mutex to protect it. (In fact i_mapping.private_lock is the usual lock for private_list). So from a quick scan here I'm thinking that a decent fix is to remove the i_mutex locking from hugetlbfs_file_mmap(), switch hugetlbfs_file_mmap() to i_size_read/write then use a hugetlb-private lock to protect i_mapping->private_list. region_chg() will do GFP_KERNEL allocations under that lock, so some care is needed. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>