Re: Intermittent storage (dm-crypt?) freeze - regression 6.4->6.5

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On Tue, 31 Oct 2023, Mikulas Patocka wrote:

> 
> 
> On Tue, 31 Oct 2023, Marek Marczykowski-Górecki wrote:
> 
> > On Tue, Oct 31, 2023 at 03:01:36PM +0100, Jan Kara wrote:
> > > On Tue 31-10-23 04:48:44, Marek Marczykowski-Górecki wrote:
> > > > Then tried:
> > > >  - PAGE_ALLOC_COSTLY_ORDER=4, order=4 - cannot reproduce,
> > > >  - PAGE_ALLOC_COSTLY_ORDER=4, order=5 - cannot reproduce,
> > > >  - PAGE_ALLOC_COSTLY_ORDER=4, order=6 - freeze rather quickly
> > > > 
> > > > I've retried the PAGE_ALLOC_COSTLY_ORDER=4,order=5 case several times
> > > > and I can't reproduce the issue there. I'm confused...
> > > 
> > > And this kind of confirms that allocations > PAGE_ALLOC_COSTLY_ORDER
> > > causing hangs is most likely just a coincidence. Rather something either in
> > > the block layer or in the storage driver has problems with handling bios
> > > with sufficiently high order pages attached. This is going to be a bit
> > > painful to debug I'm afraid. How long does it take for you trigger the
> > > hang? I'm asking to get rough estimate how heavy tracing we can afford so
> > > that we don't overwhelm the system...
> > 
> > Sometimes it freezes just after logging in, but in worst case it takes
> > me about 10min of more or less `tar xz` + `dd`.
> 
> Hi
> 
> I would like to ask you to try this patch. Revert the changes to "order" 
> and "PAGE_ALLOC_COSTLY_ORDER" back to normal and apply this patch on a 
> clean upstream kernel.
> 
> Does it deadlock?
> 
> There is a bug in dm-crypt that it doesn't account large pages in 
> cc->n_allocated_pages, this patch fixes the bug.
> 
> Mikulas

If the previous patch didn't fix it, try this patch (on a clean upstream 
kernel).

This patch allocates large pages, but it breaks them up into single-page 
entries when adding them to the bio.

If this patch deadlocks, it is a sign that allocating large pages causes 
the problem.

If this patch doesn't deadlock, it is a sign that processing a bio with 
large pages is the problem.

Mikulas

---
 drivers/md/dm-crypt.c |   26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

Index: linux-stable/drivers/md/dm-crypt.c
===================================================================
--- linux-stable.orig/drivers/md/dm-crypt.c	2023-10-31 17:16:03.000000000 +0100
+++ linux-stable/drivers/md/dm-crypt.c	2023-10-31 17:21:14.000000000 +0100
@@ -1700,11 +1700,16 @@ retry:
 		order = min(order, remaining_order);
 
 		while (order > 0) {
+			if (unlikely(percpu_counter_read_positive(&cc->n_allocated_pages) + (1 << order) > dm_crypt_pages_per_client))
+				goto decrease_order;
 			pages = alloc_pages(gfp_mask
 				| __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN | __GFP_COMP,
 				order);
-			if (likely(pages != NULL))
+			if (likely(pages != NULL)) {
+				percpu_counter_add(&cc->n_allocated_pages, 1 << order);
 				goto have_pages;
+			}
+decrease_order:
 			order--;
 		}
 
@@ -1719,8 +1724,13 @@ retry:
 
 have_pages:
 		size_to_add = min((unsigned)PAGE_SIZE << order, remaining_size);
-		__bio_add_page(clone, pages, size_to_add, 0);
 		remaining_size -= size_to_add;
+		while (size_to_add) {
+			unsigned this_step = min(size_to_add, (unsigned)PAGE_SIZE);
+			__bio_add_page(clone, pages, this_step, 0);
+			size_to_add -= this_step;
+			pages++;
+		}
 	}
 
 	/* Allocate space for integrity tags */
@@ -1739,13 +1749,21 @@ have_pages:
 static void crypt_free_buffer_pages(struct crypt_config *cc, struct bio *clone)
 {
 	struct folio_iter fi;
+	unsigned skip = 0;
 
 	if (clone->bi_vcnt > 0) { /* bio_for_each_folio_all crashes with an empty bio */
 		bio_for_each_folio_all(fi, clone) {
-			if (folio_test_large(fi.folio))
+			if (skip) {
+				skip--;
+				continue;
+			}
+			if (folio_test_large(fi.folio)) {
+				skip = (1 << folio_order(fi.folio)) - 1;
+				percpu_counter_sub(&cc->n_allocated_pages, 1 << folio_order(fi.folio));
 				folio_put(fi.folio);
-			else
+			} else {
 				mempool_free(&fi.folio->page, &cc->page_pool);
+			}
 		}
 	}
 }

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