ext4: Fix ext4_mb_initialize_context() to initialize all fields

Pavel Roskin pointed out that kmemcheck indicated that
ext4_mb_store_history() was accessing uninitialized values of
ac->ac_tail and ac->ac_buddy leading to garbage in the mballoc
history.  Fix this by initializing the entire structure to all zeros
first.

Also, two fields were getting doubly initialized by the caller of
ext4_mb_initialize_context, so remove them for efficiency's sake.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 2fcaf286f1de3b778b1df53a1bf168ae400908db..cd258463e2a9e017f949367b403d87332e5a3d24 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4227,14 +4227,9 @@ ext4_mb_initialize_context(struct ext4_allocation_context *ac,
        ext4_get_group_no_and_offset(sb, goal, &group, &block);
 
        /* set up allocation goals */
+       memset(ac, 0, sizeof(struct ext4_allocation_context));
        ac->ac_b_ex.fe_logical = ar->logical;
-       ac->ac_b_ex.fe_group = 0;
-       ac->ac_b_ex.fe_start = 0;
-       ac->ac_b_ex.fe_len = 0;
        ac->ac_status = AC_STATUS_CONTINUE;
-       ac->ac_groups_scanned = 0;
-       ac->ac_ex_scanned = 0;
-       ac->ac_found = 0;
        ac->ac_sb = sb;
        ac->ac_inode = ar->inode;
        ac->ac_o_ex.fe_logical = ar->logical;
@@ -4245,15 +4240,7 @@ ext4_mb_initialize_context(struct ext4_allocation_context *ac,
        ac->ac_g_ex.fe_group = group;
        ac->ac_g_ex.fe_start = block;
        ac->ac_g_ex.fe_len = len;
-       ac->ac_f_ex.fe_len = 0;
        ac->ac_flags = ar->flags;
-       ac->ac_2order = 0;
-       ac->ac_criteria = 0;
-       ac->ac_pa = NULL;
-       ac->ac_bitmap_page = NULL;
-       ac->ac_buddy_page = NULL;
-       ac->alloc_semp = NULL;
-       ac->ac_lg = NULL;
 
        /* we have to define context: we'll we work with a file or
         * locality group. this is a policy, actually */
@@ -4521,10 +4508,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
        }
 
        ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
-       if (ac) {
-               ac->ac_sb = sb;
-               ac->ac_inode = ar->inode;
-       } else {
+       if (!ac) {
                ar->len = 0;
                *errp = -ENOMEM;
                goto out1;