On 3/4/25 19:05, Matthew Wilcox wrote:
On Tue, Mar 04, 2025 at 04:53:09PM +0000, Matthew Wilcox wrote:
Right, that's what happened in the block layer. We mark the bio with
BIO_PAGE_PINNED if the pincount needs to be dropped. As a transitional
period, we had BIO_PAGE_REFFED which indicated that the page refcount
needed to be dropped. Perhaps there's something similar that network
could be doing.
Until that time ... how does this look as a quick hack to avoid
reverting the slab change?
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d6fed25243c3..ca08a923ac6d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1520,7 +1520,10 @@ static inline void folio_get(struct folio *folio)
static inline void get_page(struct page *page)
{
- folio_get(page_folio(page));
+ struct folio *folio = page_folio(page);
+ if (WARN_ON_ONCE(folio_test_slab(folio)))
+ return;
+ folio_get(folio);
}
static inline __must_check bool try_get_page(struct page *page)
@@ -1614,6 +1617,8 @@ static inline void put_page(struct page *page)
{
struct folio *folio = page_folio(page);
+ if (folio_test_slab(folio))
+ return;
folio_put(folio);
}
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 65f550cb5081..8c7fdb7d8c8f 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1190,8 +1190,12 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
if (!n)
return -ENOMEM;
p = *pages;
- for (int k = 0; k < n; k++)
- get_page(p[k] = page + k);
+ for (int k = 0; k < n; k++) {
+ struct folio *folio = page_folio(page);
+ p[k] = page + k;
+ if (!folio_test_slab(folio))
+ folio_get(folio);
+ }
maxsize = min_t(size_t, maxsize, n * PAGE_SIZE - *start);
i->count -= maxsize;
i->iov_offset += maxsize;
Good news and bad news ...
Good news: TLS works again!
Bad news: no errors.
Question to the wise: this is not the only place in iov_iter.c where we
do a 'get_page()'. Do we leave them and wait for others to report
regressions, knowing fully well that the current code _has_ issues?
Or shouldn't we rather clean them up?
I guess the real fix would be to fiddle with the 'bio_add_page()' logic;
we are always adding a 'page' reference to the bio, completely ignoring
whether this page is a slab page or a normal one.
Discussion at LSF, maybe?
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich
