Hi John, On 2017/11/21 8:58, Changwei Ge wrote: > Hi John, > It's better to paste your patch directly into message body. It's easy > for reviewing. > > So I copied your patch below: > >> The dw_zero_count tracking was assuming that w_unwritten_list would >> always contain one element. The actual count is now tracked whenever >> the list is extended. >> --- >> fs/ocfs2/aops.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c >> index 88a31e9340a0..eb0a81368dbb 100644 >> --- a/fs/ocfs2/aops.c >> +++ b/fs/ocfs2/aops.c >> @@ -784,6 +784,8 @@ struct ocfs2_write_ctxt { >> struct ocfs2_cached_dealloc_ctxt w_dealloc; >> >> struct list_head w_unwritten_list; >> + >> + unsigned int w_unwritten_count; >> }; >> >> void ocfs2_unlock_and_free_pages(struct page **pages, int num_pages) >> @@ -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. > >> >> *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? > > Thanks, > Changwei > >> new = NULL; >> unlock: >> spin_unlock(&oi->ip_lock); >> @@ -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;
I prefer using a loop to calculate 'dwc->dw_zero_count' rather than introducing a new variable as below: list_for_each(iter, &wc->w_unwritten_list) dwc->dw_zero_count++; thanks, Jun >> } >> >> ret = ocfs2_write_end_nolock(inode->i_mapping, pos, len, len, wc); >> -- >> 2.11.0 > > > > On 2017/11/21 2:56, John Lightsey wrote: >> In January Ben Hutchings reported Debian bug 841144 to the ocfs2-devel >> list: >> >> https://oss.oracle.com/pipermail/ocfs2-devel/2017-January/012701.html >> >> cPanel encountered this bug after upgrading our cluster to the 4.9 >> Debian stable kernel. In our environment, the bug would trigger every >> few hours. >> >> The core problem seems to be that the size of dw_zero_list is not >> tracked correctly. This causes the ocfs2_lock_allocators() call in >> ocfs2_dio_end_io_write() to underestimate the number of extents needed. >> As a result, meta_ac is null when it's needed in ocfs2_grow_tree(). >> >> The attached patch is a forward-ported version of the fix we applied to >> Debian's 4.9 kernel to correct the issue. >> > > > _______________________________________________ > Ocfs2-devel mailing list > Ocfs2-devel@oss.oracle.com > https://oss.oracle.com/mailman/listinfo/ocfs2-devel > _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel