On Thu 01-12-16 16:27:04, Ross Zwisler wrote: > On Thu, Dec 01, 2016 at 03:24:47PM -0700, Ross Zwisler wrote: > > On Thu, Nov 24, 2016 at 10:46:35AM +0100, Jan Kara wrote: > > > Currently ->iomap_begin() handler is called with entry lock held. If the > > > filesystem held any locks between ->iomap_begin() and ->iomap_end() > > > (such as ext4 which will want to hold transaction open), this would cause > > > lock inversion with the iomap_apply() from standard IO path which first > > > calls ->iomap_begin() and only then calls ->actor() callback which grabs > > > entry locks for DAX. > > > > I don't see the dax_iomap_actor() grabbing any entry locks for DAX? Is this > > an issue currently, or are you just trying to make the code consistent so we > > don't run into issues in the future? > > Ah, I see that you use this new ordering in patch 6/6 so that you can change > your interaction with the ext4 journal. I'm still curious if we have a lock > ordering inversion within DAX, but if this ordering helps you with ext4, good > enough. > > One quick comment: > > > @@ -1337,19 +1353,10 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address, > > */ > > entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD); > > if (IS_ERR(entry)) > > - goto fallback; > > + goto finish_iomap; > > > > - /* > > - * Note that we don't use iomap_apply here. We aren't doing I/O, only > > - * setting up a mapping, so really we're using iomap_begin() as a way > > - * to look up our filesystem block. > > - */ > > - pos = (loff_t)pgoff << PAGE_SHIFT; > > - error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap); > > - if (error) > > - goto unlock_entry; > > if (iomap.offset + iomap.length < pos + PMD_SIZE) > > - goto finish_iomap; > > + goto unlock_entry; > > I think this offset+length bounds check could be moved along with the > iomap_begin() call up above the grab_mapping_entry(). You would then goto > 'finish_iomap' if you hit this error condition, allowing you to avoid grabbing > and releasing of the mapping entry. Yes, that is nicer. Changed. > Other than that one small nit, this looks fine to me: > Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Thanks. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- 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
