On Tue 22-03-11 12:23:01, Darrick J. Wong wrote: > On Fri, Mar 18, 2011 at 08:28:26PM -0600, Andreas Dilger wrote: > > This seems like the best solution, IMHO, to ensure that mmap is blocked in > > page_mkwrite() before it has any chance to dirty the page undergoing > > checksum. The trick is that you need to set_page_writeback() before setting > > the page read-only, otherwise the race still exists. > > I figured out that the recursive locking errors only happened in the > set_memory_rw half of the ro/rw memory pair, and that I could make them go away > (for now) by do set_memory_rw in the kintegrityd workqueue. Then I added a > call to set_page_writeback just prior to the set_memory_ro call, though that > resulted in a lot of complaints about invalid page states and the like. It > would seem that the memory pages that arrive in bio_integrity_prep from jbd2 > don't have the writeback flag set, and setting it causes problems for it. The > writeback flag is set on all the pages that are associated with a checksum > failure, I noticed. Yeah, pages submitted by jbd2 don't have writeback flag set because they are metadata blocks written directly via buffer heads. But as you noted, these are protected in a different way by the journalling layer so shouldn't need to worry. > As for changing pte's around... does that set_memory_ro change the pte flags > for all running processes? I'm not so sure it does for anything other than the > current process. I think I saw a flush_tlb call in there... though I don't > think it helps me much. > > If I /don't/ set the flag, the frequency of the errors decreases further to > about once an hour, but I still see the occasional error. :/ Currently I'm > trying to figure out how one might distinguish dirty pages that shouldn't have > writeback set vs. pages that ought to have it but don't. It's difficult at the block layer... If page->mapping->host is not a device inode, the page should have PageWriteback set. If it is a device inode, you don't know - JBD2 will submit pages without PageWriteback set, flusher thread will submit pages with PageWriteback set. And both is OK since we use buffer state for synchronization. Honza -- Jan Kara <jack@xxxxxxx> 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
