Re: Crashes/hung tasks with z3pool under memory pressure

[Vitaly Wool]

Hey Guenter,

On 04/13/2018 07:56 PM, Guenter Roeck wrote:
On Fri, Apr 13, 2018 at 05:40:18PM +0000, Vitaly Wool wrote:
On Fri, Apr 13, 2018, 7:35 PM Guenter Roeck <li...@roeck-us.net> wrote:

On Fri, Apr 13, 2018 at 05:21:02AM +0000, Vitaly Wool wrote:
Hi Guenter,


Den fre 13 apr. 2018 kl 00:01 skrev Guenter Roeck <li...@roeck-us.net>:

Hi all,
we are observing crashes with z3pool under memory pressure. The kernel
version
used to reproduce the problem is v4.16-11827-g5d1365940a68, but the
problem was
also seen with v4.14 based kernels.

just before I dig into this, could you please try reproducing the errors
you see with https://patchwork.kernel.org/patch/10210459/ applied?

As mentioned above, I tested with v4.16-11827-g5d1365940a68, which already
includes this patch.

Bah. Sorry. Expect an update after the weekend.

NP; easy to miss. Thanks a lot for looking into it.

I wonder if the following patch would make a difference:

diff --git a/mm/z3fold.c b/mm/z3fold.c
index c0bca6153b95..5e547c2d5832 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -887,19 +887,21 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, 
unsigned int retries)
                                goto next;
                }
 next:
-               spin_lock(&pool->lock);
                if (test_bit(PAGE_HEADLESS, &page->private)) {
                        if (ret == 0) {
-                               spin_unlock(&pool->lock);
                                free_z3fold_page(page);
                                return 0;
                        }
-               } else if (kref_put(&zhdr->refcount, release_z3fold_page)) {
-                       atomic64_dec(&pool->pages_nr);
-                       spin_unlock(&pool->lock);
-                       return 0;
+               } else {
+                       spin_lock(&zhdr->page_lock);
+                       if (kref_put(&zhdr->refcount, 
release_z3fold_page_locked)) {
+                               atomic64_dec(&pool->pages_nr);
+                               return 0;
+                       }
+                       spin_unlock(&zhdr->page_lock);
                }
 
+		spin_lock(&pool->lock);
                /*
                 * Add to the beginning of LRU.
                 * Pool lock has to be kept here to ensure the page has


Thanks,
   Vitaly