On 2017/11/21 10:45, John Lightsey wrote: > On Tue, 2017-11-21 at 00:58 +0000, Changwei Ge wrote: >>> @@ -873,6 +875,7 @@ static int ocfs2_alloc_write_ctxt(struct >>> ocfs2_write_ctxt **wcp, >>> >>> ocfs2_init_dealloc_ctxt(&wc->w_dealloc); >>> INIT_LIST_HEAD(&wc->w_unwritten_list); >>> + wc->w_unwritten_count = 0; >> >> I think you don't have to evaluate ::w_unwritten_count to zero since >> kzalloc already did that. > > Very true. I was following the example of how dwc was handling the > dw_zero_count. You'll have to forgive me a bit. I'm very unfamiliar > with the linux kernel codebase. > >> >>> >>> *wcp = wc; >>> >>> @@ -1373,6 +1376,7 @@ static int ocfs2_unwritten_check(struct inode >>> *inode, >>> desc->c_clear_unwritten = 0; >>> list_add_tail(&new->ue_ip_node, &oi->ip_unwritten_list); >>> list_add_tail(&new->ue_node, &wc->w_unwritten_list); >>> + wc->w_unwritten_count++; >> >> You increase ::w_unwritten_coun once a new _ue_ is attached to >> ::w_unwritten_list. So if no _ue_ ever is attached, >> ::w_unwritten_list >> is still empty. I think your change has the same effect with origin. >> >> Moreover I don't see the relation between the reported crash issue >> and your patch change. Can you elaborate further? > > The important part is in the next segment in the patch. This block is > just using w_unwritten_count to track the size of w_unwritten_list. > >>> @@ -2246,7 +2250,7 @@ static int ocfs2_dio_get_block(struct inode >>> *inode, sector_t iblock, >>> ue->ue_phys = desc->c_phys; >>> >>> list_splice_tail_init(&wc->w_unwritten_list, >>> &dwc->dw_zero_list); >>> - dwc->dw_zero_count++; >>> + dwc->dw_zero_count += wc->w_unwritten_count; >>> } >>> >>> > > dw_zero_count is tracking the number of elements in dw_zero_list. > > The old version assumed that after dw_zero_list and w_unwritten_list > were spliced together, that the new length was dw_zero_count + 1. This > assumption is not correct if w_unwritten_list contained more than one > element. > > The length of dw_zero_list is used by ocfs2_dio_end_io_write() to > determine whether or not meta_ac will be needed to complete the write: > > ret = ocfs2_lock_allocators(inode, &et, 0, dwc->dw_zero_count*2, > &data_ac, &meta_ac); Hi John,
Thanks for reporting. I probably get your point. Can your tell me how did you format your volume? What's your _cluster size_ and _block size_? Your can obtain such information via debugfs.ocfs2 <your volume> -R 'stats' | grep 'Cluster Size' It's better for you provide a way to reproduce this issue so that we can perform some test. Thanks, Changwei > > This will return with success and a null meta_ac if there are at least > dw_zero_count * 2 extents available for the write. > > Since dw_zero_count was not being calculated correctly, this will > occasionally result in the write getting into ocfs2_grow_tree() with a > null meta_ac following this chain: > > ocfs2_dio_end_io_write() > ocfs2_mark_extent_written() > ocfs2_change_extent_flag() > ocfs2_split_extent() > ocfs2_split_and_insert() > ocfs2_grow_tree() > > That's my understanding of what's causing the bug. > > Our OCFS2 cluster was crashing every two to three hours after we > upgraded to a 4.x kernel. We've gone about 18 hours with this patch > applied and no crashes. > _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel
