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ext4: mballoc: add blocks to PA list under same spinlock after allocating blocks
ext4_mb_discard_preallocations() only checks for grp->bb_prealloc_list of every group to discard the group's PA to free up the space if allocation request fails. Consider below race:- Process A Process B 1. allocate blocks 1. Fails block allocation from ext4_mb_regular_allocator() ext4_lock_group() allocated blocks more than ac_o_ex.fe_len ext4_unlock_group() 2. Scans the grp->bb_prealloc_list (under ext4_lock_group()) and find nothing and thus return -ENOSPC. 2. Add the additional blocks to PA list ext4_lock_group() add blocks to grp->bb_prealloc_list ext4_unlock_group() Above race could be avoided if we add those additional blocks to grp->bb_prealloc_list at the same time with block allocation when ext4_lock_group() was still held. With this discard-PA will know if there are actually any blocks which could be freed from the PA Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com> Link: https://lore.kernel.org/r/a2217dd782585b42328981832e6d396abaaccb80.1589955723.git.riteshh@linux.ibm.com Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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@ -349,6 +349,7 @@ static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
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ext4_group_t group);
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static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
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ext4_group_t group);
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static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);
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static inline void *mb_correct_addr_and_bit(int *bit, void *addr)
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{
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@ -1701,6 +1702,14 @@ static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
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sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
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spin_unlock(&sbi->s_md_lock);
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}
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/*
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* As we've just preallocated more space than
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* user requested originally, we store allocated
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* space in a special descriptor.
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*/
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if (ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
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ext4_mb_new_preallocation(ac);
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}
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/*
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@ -1949,7 +1958,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
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ext4_mb_use_best_found(ac, e4b);
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BUG_ON(ac->ac_b_ex.fe_len != ac->ac_g_ex.fe_len);
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BUG_ON(ac->ac_f_ex.fe_len != ac->ac_g_ex.fe_len);
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if (EXT4_SB(sb)->s_mb_stats)
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atomic_inc(&EXT4_SB(sb)->s_bal_2orders);
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@ -3675,7 +3684,7 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
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/*
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* creates new preallocated space for given inode
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*/
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static noinline_for_stack int
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static noinline_for_stack void
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ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
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{
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struct super_block *sb = ac->ac_sb;
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@ -3688,10 +3697,9 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
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BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
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BUG_ON(ac->ac_status != AC_STATUS_FOUND);
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BUG_ON(!S_ISREG(ac->ac_inode->i_mode));
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BUG_ON(ac->ac_pa == NULL);
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pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
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if (pa == NULL)
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return -ENOMEM;
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pa = ac->ac_pa;
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if (ac->ac_b_ex.fe_len < ac->ac_g_ex.fe_len) {
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int winl;
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@ -3735,7 +3743,6 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
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pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
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pa->pa_len = ac->ac_b_ex.fe_len;
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pa->pa_free = pa->pa_len;
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atomic_set(&pa->pa_count, 1);
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spin_lock_init(&pa->pa_lock);
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INIT_LIST_HEAD(&pa->pa_inode_list);
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INIT_LIST_HEAD(&pa->pa_group_list);
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@ -3755,21 +3762,17 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
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pa->pa_obj_lock = &ei->i_prealloc_lock;
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pa->pa_inode = ac->ac_inode;
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ext4_lock_group(sb, ac->ac_b_ex.fe_group);
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list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
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ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
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spin_lock(pa->pa_obj_lock);
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list_add_rcu(&pa->pa_inode_list, &ei->i_prealloc_list);
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spin_unlock(pa->pa_obj_lock);
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return 0;
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}
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/*
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* creates new preallocated space for locality group inodes belongs to
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*/
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static noinline_for_stack int
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static noinline_for_stack void
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ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
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{
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struct super_block *sb = ac->ac_sb;
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@ -3781,11 +3784,9 @@ ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
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BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
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BUG_ON(ac->ac_status != AC_STATUS_FOUND);
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BUG_ON(!S_ISREG(ac->ac_inode->i_mode));
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BUG_ON(ac->ac_pa == NULL);
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BUG_ON(ext4_pspace_cachep == NULL);
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pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
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if (pa == NULL)
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return -ENOMEM;
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pa = ac->ac_pa;
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/* preallocation can change ac_b_ex, thus we store actually
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* allocated blocks for history */
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@ -3795,7 +3796,6 @@ ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
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pa->pa_lstart = pa->pa_pstart;
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pa->pa_len = ac->ac_b_ex.fe_len;
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pa->pa_free = pa->pa_len;
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atomic_set(&pa->pa_count, 1);
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spin_lock_init(&pa->pa_lock);
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INIT_LIST_HEAD(&pa->pa_inode_list);
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INIT_LIST_HEAD(&pa->pa_group_list);
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@ -3816,26 +3816,20 @@ ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
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pa->pa_obj_lock = &lg->lg_prealloc_lock;
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pa->pa_inode = NULL;
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ext4_lock_group(sb, ac->ac_b_ex.fe_group);
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list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
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ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
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/*
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* We will later add the new pa to the right bucket
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* after updating the pa_free in ext4_mb_release_context
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*/
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return 0;
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}
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static int ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
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static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
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{
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int err;
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if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
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err = ext4_mb_new_group_pa(ac);
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ext4_mb_new_group_pa(ac);
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else
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err = ext4_mb_new_inode_pa(ac);
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return err;
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ext4_mb_new_inode_pa(ac);
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}
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/*
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@ -4150,6 +4144,29 @@ repeat:
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}
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}
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static int ext4_mb_pa_alloc(struct ext4_allocation_context *ac)
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{
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struct ext4_prealloc_space *pa;
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BUG_ON(ext4_pspace_cachep == NULL);
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pa = kmem_cache_zalloc(ext4_pspace_cachep, GFP_NOFS);
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if (!pa)
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return -ENOMEM;
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atomic_set(&pa->pa_count, 1);
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ac->ac_pa = pa;
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return 0;
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}
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static void ext4_mb_pa_free(struct ext4_allocation_context *ac)
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{
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struct ext4_prealloc_space *pa = ac->ac_pa;
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BUG_ON(!pa);
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ac->ac_pa = NULL;
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WARN_ON(!atomic_dec_and_test(&pa->pa_count));
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kmem_cache_free(ext4_pspace_cachep, pa);
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}
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#ifdef CONFIG_EXT4_DEBUG
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static inline void ext4_mb_show_pa(struct super_block *sb)
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{
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@ -4606,23 +4623,28 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
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if (!ext4_mb_use_preallocated(ac)) {
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ac->ac_op = EXT4_MB_HISTORY_ALLOC;
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ext4_mb_normalize_request(ac, ar);
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*errp = ext4_mb_pa_alloc(ac);
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if (*errp)
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goto errout;
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repeat:
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/* allocate space in core */
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*errp = ext4_mb_regular_allocator(ac);
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if (*errp)
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goto discard_and_exit;
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/* as we've just preallocated more space than
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* user requested originally, we store allocated
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* space in a special descriptor */
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if (ac->ac_status == AC_STATUS_FOUND &&
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ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
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*errp = ext4_mb_new_preallocation(ac);
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/*
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* pa allocated above is added to grp->bb_prealloc_list only
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* when we were able to allocate some block i.e. when
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* ac->ac_status == AC_STATUS_FOUND.
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* And error from above mean ac->ac_status != AC_STATUS_FOUND
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* So we have to free this pa here itself.
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*/
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if (*errp) {
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discard_and_exit:
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ext4_mb_pa_free(ac);
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ext4_discard_allocated_blocks(ac);
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goto errout;
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}
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if (ac->ac_status == AC_STATUS_FOUND &&
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ac->ac_o_ex.fe_len >= ac->ac_f_ex.fe_len)
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ext4_mb_pa_free(ac);
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}
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if (likely(ac->ac_status == AC_STATUS_FOUND)) {
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*errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
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@ -4637,6 +4659,11 @@ repeat:
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freed = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
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if (freed)
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goto repeat;
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/*
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* If block allocation fails then the pa allocated above
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* needs to be freed here itself.
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*/
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ext4_mb_pa_free(ac);
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*errp = -ENOSPC;
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}
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