read_mapping() breaks on NR_CPUS not div by 32

This patch fixes a bug in read_mapping(), which is used for
reading CPU and cluster (domain) mappings. read_mapping()
did not account for the case when NR_CPUS is not evenly
divisible by 32 (quite common when NR_CPUS < 32).

1 files changed, 13 insertions, 7 deletions

diff --git a/src/migration.c b/src/migration.c
index ae7761b..1316d4c 100644
--- a/src/migration.c
+++ b/src/migration.c
@@ -48,14 +48,16 @@ static int read_mapping(int idx, const char* which, cpu_set_t** set, size_t *sz)
         if (num_online_cpus() > 4096)
                 goto out;
 
+        /* Read string is in the format of <mask>[,<mask>]*. All <mask>s following
+           a comma are 8 chars (representing a 32-bit mask). The first <mask> may
+           have fewer chars. Bits are MSB to LSB, left to right. */
         snprintf(fname, sizeof(fname), "/proc/litmus/%s/%d", which, idx);
-
         ret = read_file(fname, &buf, sizeof(buf)-1);
         if (ret <= 0)
                 goto out;
 
         len = strnlen(buf, sizeof(buf));
-        nbits = 32*(len/9 + 1); /* buf is a series of comma + 32-bits as hex */
+        nbits = 32*(len/9) + 4*(len%9); /* compute bits, accounting for commas */
 
         *set = CPU_ALLOC(nbits);
         *sz = CPU_ALLOC_SIZE(nbits);
@@ -64,17 +66,21 @@ static int read_mapping(int idx, const char* which, cpu_set_t** set, size_t *sz)
         /* process LSB chunks first (at the end of the str) and move backward */
         chunk_str = buf + len - 8;
         i = 0;
-        while (chunk_str >= buf) {
-                unsigned long chunk = strtoul(chunk_str, NULL, 16);
+        do
+        {
+                unsigned long chunk;
+                if(chunk_str < buf)
+                        chunk_str = buf; /* when MSB mask is less than 8 chars */
+                chunk = strtoul(chunk_str, NULL, 16);
                 while (chunk) {
                         int j = ffsl(chunk) - 1;
-                        CPU_SET_S(i*32 + j, *sz, *set);
+                        int x = i*32 + j;
+                        CPU_SET_S(x, *sz, *set);
                         chunk &= ~(1ul << j);
                 }
-
                 chunk_str -= 9;
                 i += 1;
-        }
+        } while(chunk_str >= buf - 8);
 
         ret = 0;