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); 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.
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