Showing error 896

User: Jiri Slaby
Error type: Double Lock
Error type description: Some lock is locked twice unintentionally in a sequence
File location: fs/ext4/mballoc.c
Line in file: 4189
Project: Linux Kernel
Project version: 2.6.28
Tools: Undetermined 1
Stanse (1.2)
Entered: 2012-02-27 21:22:42 UTC

Source: 

4159                call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
4160        }
4161        if (ac)
4162                kmem_cache_free(ext4_ac_cachep, ac);
4163}
4164
4165/*
4166 * We have incremented pa_count. So it cannot be freed at this
4167 * point. Also we hold lg_mutex. So no parallel allocation is
4168 * possible from this lg. That means pa_free cannot be updated.
4169 *
4170 * A parallel ext4_mb_discard_group_preallocations is possible.
4171 * which can cause the lg_prealloc_list to be updated.
4172 */
4173
4174static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
4175{
4176        int order, added = 0, lg_prealloc_count = 1;
4177        struct super_block *sb = ac->ac_sb;
4178        struct ext4_locality_group *lg = ac->ac_lg;
4179        struct ext4_prealloc_space *tmp_pa, *pa = ac->ac_pa;
4180
4181        order = fls(pa->pa_free) - 1;
4182        if (order > PREALLOC_TB_SIZE - 1)
4183                /* The max size of hash table is PREALLOC_TB_SIZE */
4184                order = PREALLOC_TB_SIZE - 1;
4185        /* Add the prealloc space to lg */
4186        rcu_read_lock();
4187        list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
4188                                                pa_inode_list) {
4189                spin_lock(&tmp_pa->pa_lock);
4190                if (tmp_pa->pa_deleted) {
4191                        spin_unlock(&pa->pa_lock);
4192                        continue;
4193                }
4194                if (!added && pa->pa_free < tmp_pa->pa_free) {
4195                        /* Add to the tail of the previous entry */
4196                        list_add_tail_rcu(&pa->pa_inode_list,
4197                                                &tmp_pa->pa_inode_list);
4198                        added = 1;
4199                        /*
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