mm, mempolicy: make mpol_to_str robust and always succeed

mpol_to_str() should not fail.  Currently, it either fails because the
string buffer is too small or because a string hasn't been defined for a
mempolicy mode.

If a new mempolicy mode is introduced and no string is defined for it,
just warn and return "unknown".

If the buffer is too small, just truncate the string and return, the
same behavior as snprintf().

This also fixes a bug where there was no NULL-byte termination when doing
*p++ = '=' and *p++ ':' and maxlen has been reached.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Chen Gang <gang.chen@asianux.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 390bdab01c3c782cc14b55c6d1ef35ebddcc4197..9f1369fe0afbfc10524636cb6c67bf4f52b8f3b5 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1387,8 +1387,8 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
        struct mm_struct *mm = vma->vm_mm;
        struct mm_walk walk = {};
        struct mempolicy *pol;
-       int n;
-       char buffer[50];
+       char buffer[64];
+       int nid;
 
        if (!mm)
                return 0;
@@ -1404,10 +1404,8 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
        walk.mm = mm;
 
        pol = get_vma_policy(task, vma, vma->vm_start);
-       n = mpol_to_str(buffer, sizeof(buffer), pol);
+       mpol_to_str(buffer, sizeof(buffer), pol);
        mpol_cond_put(pol);
-       if (n < 0)
-               return n;
 
        seq_printf(m, "%08lx %s", vma->vm_start, buffer);
 
@@ -1460,9 +1458,9 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
        if (md->writeback)
                seq_printf(m, " writeback=%lu", md->writeback);
 
-       for_each_node_state(n, N_MEMORY)
-               if (md->node[n])
-                       seq_printf(m, " N%d=%lu", n, md->node[n]);
+       for_each_node_state(nid, N_MEMORY)
+               if (md->node[nid])
+                       seq_printf(m, " N%d=%lu", nid, md->node[nid]);
 out:
        seq_putc(m, '\n');
 

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index ea4d2495c6464bb2a5789f2566358461cca31330..9fe426b30a418e335485a7aee045883c974f15de 100644 (file)
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -169,7 +169,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 extern int mpol_parse_str(char *str, struct mempolicy **mpol);
 #endif
 
-extern int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol);
+extern void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol);
 
 /* Check if a vma is migratable */
 static inline int vma_migratable(struct vm_area_struct *vma)
@@ -307,9 +307,8 @@ static inline int mpol_parse_str(char *str, struct mempolicy **mpol)
 }
 #endif
 
-static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
+static inline void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 {
-       return 0;
 }
 
 static inline int mpol_misplaced(struct page *page, struct vm_area_struct *vma,

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 71cb253368cb72b1bf99d390ca9360ccc277c29b..260b8213a8733f861a51b656a92cffb0a0bb9731 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2914,62 +2914,45 @@ out:
  * @maxlen:  length of @buffer
  * @pol:  pointer to mempolicy to be formatted
  *
- * Convert a mempolicy into a string.
- * Returns the number of characters in buffer (if positive)
- * or an error (negative)
+ * Convert @pol into a string.  If @buffer is too short, truncate the string.
+ * Recommend a @maxlen of at least 32 for the longest mode, "interleave", the
+ * longest flag, "relative", and to display at least a few node ids.
  */
-int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
+void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 {
        char *p = buffer;
-       int l;
-       nodemask_t nodes;
-       unsigned short mode;
-       unsigned short flags = pol ? pol->flags : 0;
-
-       /*
-        * Sanity check:  room for longest mode, flag and some nodes
-        */
-       VM_BUG_ON(maxlen < strlen("interleave") + strlen("relative") + 16);
+       nodemask_t nodes = NODE_MASK_NONE;
+       unsigned short mode = MPOL_DEFAULT;
+       unsigned short flags = 0;
 
-       if (!pol || pol == &default_policy)
-               mode = MPOL_DEFAULT;
-       else
+       if (pol && pol != &default_policy) {
                mode = pol->mode;
+               flags = pol->flags;
+       }
 
        switch (mode) {
        case MPOL_DEFAULT:
-               nodes_clear(nodes);
                break;
-
        case MPOL_PREFERRED:
-               nodes_clear(nodes);
                if (flags & MPOL_F_LOCAL)
                        mode = MPOL_LOCAL;
                else
                        node_set(pol->v.preferred_node, nodes);
                break;
-
        case MPOL_BIND:
-               /* Fall through */
        case MPOL_INTERLEAVE:
                nodes = pol->v.nodes;
                break;
-
        default:
-               return -EINVAL;
+               WARN_ON_ONCE(1);
+               snprintf(p, maxlen, "unknown");
+               return;
        }
 
-       l = strlen(policy_modes[mode]);
-       if (buffer + maxlen < p + l + 1)
-               return -ENOSPC;
-
-       strcpy(p, policy_modes[mode]);
-       p += l;
+       p += snprintf(p, maxlen, policy_modes[mode]);
 
        if (flags & MPOL_MODE_FLAGS) {
-               if (buffer + maxlen < p + 2)
-                       return -ENOSPC;
-               *p++ = '=';
+               p += snprintf(p, buffer + maxlen - p, "=");
 
                /*
                 * Currently, the only defined flags are mutually exclusive
@@ -2981,10 +2964,7 @@ int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
        }
 
        if (!nodes_empty(nodes)) {
-               if (buffer + maxlen < p + 2)
-                       return -ENOSPC;
-               *p++ = ':';
+               p += snprintf(p, buffer + maxlen - p, ":");
                p += nodelist_scnprintf(p, buffer + maxlen - p, nodes);
        }
-       return p - buffer;
 }