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. Other than that one small nit, this looks fine to me: Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> -- 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
