| Message ID | 153889193718.3143179.3432479794012686784.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d7782145e1ad537df4ce74e58c50f1f732a1462d |
| Headers | show |
| Series | [v2] filesystem-dax: Fix dax_layout_busy_page() livelock | expand |
On Sat 06-10-18 22:59:56, Dan Williams wrote: > In the presence of multi-order entries the typical > pagevec_lookup_entries() pattern may loop forever: > > while (index < end && pagevec_lookup_entries(&pvec, mapping, index, > min(end - index, (pgoff_t)PAGEVEC_SIZE), > indices)) { > ... > for (i = 0; i < pagevec_count(&pvec); i++) { > index = indices[i]; > ... > } > index++; /* BUG */ > } > > The loop updates 'index' for each index found and then increments to the > next possible page to continue the lookup. However, if the last entry in > the pagevec is multi-order then the next possible page index is more > than 1 page away. Fix this locally for the filesystem-dax case by > checking for dax-multi-order entries. Going forward new users of > multi-order entries need to be similarly careful, or we need a generic > way to report the page increment in the radix iterator. > > Fixes: 5fac7408d828 ("mm, fs, dax: handle layout changes to pinned dax...") > Cc: <stable@vger.kernel.org> > Cc: Jan Kara <jack@suse.cz> > Cc: Ross Zwisler <zwisler@kernel.org> > Cc: Matthew Wilcox <willy@infradead.org> > Signed-off-by: Dan Williams <dan.j.williams@intel.com> > --- > Changes in v2: > * Only update nr_pages if the last entry in the pagevec is multi-order. > > fs/dax.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) Thanks for fixing this up! It is somewhat ugly but nicer fixes would be more intrusive so I agree with this approach for the ease of backporting and let's clean up the iteration code later. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > > diff --git a/fs/dax.c b/fs/dax.c > index 4becbf168b7f..0fb270f0a0ef 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -666,6 +666,8 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > while (index < end && pagevec_lookup_entries(&pvec, mapping, index, > min(end - index, (pgoff_t)PAGEVEC_SIZE), > indices)) { > + pgoff_t nr_pages = 1; > + > for (i = 0; i < pagevec_count(&pvec); i++) { > struct page *pvec_ent = pvec.pages[i]; > void *entry; > @@ -680,8 +682,15 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > > xa_lock_irq(&mapping->i_pages); > entry = get_unlocked_mapping_entry(mapping, index, NULL); > - if (entry) > + if (entry) { > page = dax_busy_page(entry); > + /* > + * Account for multi-order entries at > + * the end of the pagevec. > + */ > + if (i + 1 >= pagevec_count(&pvec)) > + nr_pages = 1UL << dax_radix_order(entry); > + } > put_unlocked_mapping_entry(mapping, index, entry); > xa_unlock_irq(&mapping->i_pages); > if (page) > @@ -696,7 +705,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > */ > pagevec_remove_exceptionals(&pvec); > pagevec_release(&pvec); > - index++; > + index += nr_pages; > > if (page) > break; >
diff --git a/fs/dax.c b/fs/dax.c index 4becbf168b7f..0fb270f0a0ef 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -666,6 +666,8 @@ struct page *dax_layout_busy_page(struct address_space *mapping) while (index < end && pagevec_lookup_entries(&pvec, mapping, index, min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) { + pgoff_t nr_pages = 1; + for (i = 0; i < pagevec_count(&pvec); i++) { struct page *pvec_ent = pvec.pages[i]; void *entry; @@ -680,8 +682,15 @@ struct page *dax_layout_busy_page(struct address_space *mapping) xa_lock_irq(&mapping->i_pages); entry = get_unlocked_mapping_entry(mapping, index, NULL); - if (entry) + if (entry) { page = dax_busy_page(entry); + /* + * Account for multi-order entries at + * the end of the pagevec. + */ + if (i + 1 >= pagevec_count(&pvec)) + nr_pages = 1UL << dax_radix_order(entry); + } put_unlocked_mapping_entry(mapping, index, entry); xa_unlock_irq(&mapping->i_pages); if (page) @@ -696,7 +705,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping) */ pagevec_remove_exceptionals(&pvec); pagevec_release(&pvec); - index++; + index += nr_pages; if (page) break;
In the presence of multi-order entries the typical pagevec_lookup_entries() pattern may loop forever: while (index < end && pagevec_lookup_entries(&pvec, mapping, index, min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) { ... for (i = 0; i < pagevec_count(&pvec); i++) { index = indices[i]; ... } index++; /* BUG */ } The loop updates 'index' for each index found and then increments to the next possible page to continue the lookup. However, if the last entry in the pagevec is multi-order then the next possible page index is more than 1 page away. Fix this locally for the filesystem-dax case by checking for dax-multi-order entries. Going forward new users of multi-order entries need to be similarly careful, or we need a generic way to report the page increment in the radix iterator. Fixes: 5fac7408d828 ("mm, fs, dax: handle layout changes to pinned dax...") Cc: <stable@vger.kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Ross Zwisler <zwisler@kernel.org> Cc: Matthew Wilcox <willy@infradead.org> Signed-off-by: Dan Williams <dan.j.williams@intel.com> --- Changes in v2: * Only update nr_pages if the last entry in the pagevec is multi-order. fs/dax.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)