Fix bug in GPU list balancing

The function split_sci_entry could produce empty lists, which can
cause illegal memory access or incorrect energies. Before commit
6106367b this bug was never triggered, since nsp_max was never smaller
than a full cj4 entry. But 6106367b introduced a but that could
produce negative nsp_max.

Fixes #1767.

Change-Id: I2007cf6851f94f4f2ca62f609a0628725014dbe7

diff --git a/src/gromacs/mdlib/nbnxn_search.c b/src/gromacs/mdlib/nbnxn_search.c
index a3720823567862c8d3740ef5973d352417be082c..d10ddf70b32739badc6e19dd84afa57fdb7aee76 100644 (file)
--- a/src/gromacs/mdlib/nbnxn_search.c
+++ b/src/gromacs/mdlib/nbnxn_search.c
@@ -4014,7 +4014,8 @@ static void split_sci_entry(nbnxn_pairlist_t *nbl,
                 nsp_cj4 += (nbl->cj4[cj4].imei[0].imask >> p) & 1;
             }
 
-            if (nsp_cj4 > 0 && nsp + nsp_cj4 > nsp_max)
+            /* Check if we should split at this cj4 to get a list of size nsp */
+            if (nsp > 0 && nsp + nsp_cj4 > nsp_max)
             {
                 /* Split the list at cj4 */
                 nbl->sci[sci].cj4_ind_end = cj4;