On Wed, Apr 11, 2018 at 10:59:09AM +0300, Nikolay Borisov wrote:
> When the delayed refs for a head are all run, eventually
> cleanup_ref_head is called which (in case of deletion) obtains a
> reference for the relevant btrfs_space_info struct by querying the bg
> for the range. This is problematic because when the last extent of a
> bg is deleted a race window emerges between removal of that bg and the
> subsequent invocation of cleanup_ref_head. This can result in cache being null
> and either a null pointer dereference or assertion failure.
>
> task: ffff8d04d31ed080 task.stack: ffff9e5dc10cc000
> RIP: 0010:assfail.constprop.78+0x18/0x1a [btrfs]
> RSP: 0018:ffff9e5dc10cfbe8 EFLAGS: 00010292
> RAX: 0000000000000044 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: ffff8d04ffc1f868 RSI: ffff8d04ffc178c8 RDI: ffff8d04ffc178c8
> RBP: ffff8d04d29e5ea0 R08: 00000000000001f0 R09: 0000000000000001
> R10: ffff9e5dc0507d58 R11: 0000000000000001 R12: ffff8d04d29e5ea0
> R13: ffff8d04d29e5f08 R14: ffff8d04efe29b40 R15: ffff8d04efe203e0
> FS: 00007fbf58ead500(0000) GS:ffff8d04ffc00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fe6c6975648 CR3: 0000000013b2a000 CR4: 00000000000006f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> __btrfs_run_delayed_refs+0x10e7/0x12c0 [btrfs]
> btrfs_run_delayed_refs+0x68/0x250 [btrfs]
> btrfs_should_end_transaction+0x42/0x60 [btrfs]
> btrfs_truncate_inode_items+0xaac/0xfc0 [btrfs]
> btrfs_evict_inode+0x4c6/0x5c0 [btrfs]
> evict+0xc6/0x190
> do_unlinkat+0x19c/0x300
> do_syscall_64+0x74/0x140
> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> RIP: 0033:0x7fbf589c57a7
>
> To fix this, introduce a new flag "is_system" to head_ref structs,
> which is populated at insertion time. This allows to decouple the
> querying for the spaceinfo from querying the possibly deleted bg.
>
> Fixes: d7eae3403f46 ("Btrfs: rework delayed ref total_bytes_pinned accounting")
> Suggested-by: Omar Sandoval <osandov@xxxxxxxxxxx>
> Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
> ---
>
> v2:
> * Collapsed the if/else logic in cleanup_ref_head
>
> fs/btrfs/delayed-ref.c | 19 ++++++++++++++-----
> fs/btrfs/delayed-ref.h | 1 +
> fs/btrfs/extent-tree.c | 18 +++++++++++++-----
> 3 files changed, 28 insertions(+), 10 deletions(-)
>
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index 5ac2d7909782..20fa7b4c132d 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -550,8 +550,10 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info,
> struct btrfs_delayed_ref_head *head_ref,
> struct btrfs_qgroup_extent_record *qrecord,
> u64 bytenr, u64 num_bytes, u64 ref_root, u64 reserved,
> - int action, int is_data, int *qrecord_inserted_ret,
> + int action, int is_data, int is_system,
> + int *qrecord_inserted_ret,
> int *old_ref_mod, int *new_ref_mod)
> +
> {
> struct btrfs_delayed_ref_head *existing;
> struct btrfs_delayed_ref_root *delayed_refs;
> @@ -595,6 +597,7 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info,
> head_ref->ref_mod = count_mod;
> head_ref->must_insert_reserved = must_insert_reserved;
> head_ref->is_data = is_data;
> + head_ref->is_system = is_system;
> head_ref->ref_tree = RB_ROOT;
> INIT_LIST_HEAD(&head_ref->ref_add_list);
> RB_CLEAR_NODE(&head_ref->href_node);
> @@ -782,6 +785,7 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
> struct btrfs_delayed_ref_root *delayed_refs;
> struct btrfs_qgroup_extent_record *record = NULL;
> int qrecord_inserted;
> + int is_system = ref_root == BTRFS_CHUNK_TREE_OBJECTID;
>
> BUG_ON(extent_op && extent_op->is_data);
> ref = kmem_cache_alloc(btrfs_delayed_tree_ref_cachep, GFP_NOFS);
> @@ -810,8 +814,8 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
> */
> head_ref = add_delayed_ref_head(fs_info, trans, head_ref, record,
> bytenr, num_bytes, 0, 0, action, 0,
> - &qrecord_inserted, old_ref_mod,
> - new_ref_mod);
> + is_system, &qrecord_inserted,
> + old_ref_mod, new_ref_mod);
>
> add_delayed_tree_ref(fs_info, trans, head_ref, &ref->node, bytenr,
> num_bytes, parent, ref_root, level, action);
> @@ -878,7 +882,7 @@ int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info,
> */
> head_ref = add_delayed_ref_head(fs_info, trans, head_ref, record,
> bytenr, num_bytes, ref_root, reserved,
> - action, 1, &qrecord_inserted,
> + action, 1, 0, &qrecord_inserted,
> old_ref_mod, new_ref_mod);
>
> add_delayed_data_ref(fs_info, trans, head_ref, &ref->node, bytenr,
> @@ -908,9 +912,14 @@ int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info,
> delayed_refs = &trans->transaction->delayed_refs;
> spin_lock(&delayed_refs->lock);
>
> + /*
> + * extent_ops just modify the flags of an extent and they don't result
> + * in ref count changes, hence it's safe to pass false/0 for is_system
> + * argument
> + */
> add_delayed_ref_head(fs_info, trans, head_ref, NULL, bytenr,
> num_bytes, 0, 0, BTRFS_UPDATE_DELAYED_HEAD,
> - extent_op->is_data, NULL, NULL, NULL);
> + extent_op->is_data, 0, NULL, NULL, NULL);
>
> spin_unlock(&delayed_refs->lock);
> return 0;
> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
> index cdf4a94ce5c1..7e7bf4e66d48 100644
> --- a/fs/btrfs/delayed-ref.h
> +++ b/fs/btrfs/delayed-ref.h
> @@ -139,6 +139,7 @@ struct btrfs_delayed_ref_head {
> */
> unsigned int must_insert_reserved:1;
> unsigned int is_data:1;
> + unsigned int is_system:1;
> unsigned int processing:1;
> };
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 9a05e5b5089f..349b053680c8 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2616,13 +2616,21 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans,
> trace_run_delayed_ref_head(fs_info, head, 0);
>
> if (head->total_ref_mod < 0) {
> - struct btrfs_block_group_cache *cache;
> + struct btrfs_space_info *space_info;
>
> - cache = btrfs_lookup_block_group(fs_info, head->bytenr);
> - ASSERT(cache);
> - percpu_counter_add(&cache->space_info->total_bytes_pinned,
> + if (head->is_data) {
> + space_info = __find_space_info(fs_info,
> + BTRFS_BLOCK_GROUP_DATA);
> + } else if (head->is_system) {
> + space_info = __find_space_info(fs_info,
> + BTRFS_BLOCK_GROUP_SYSTEM);
> + } else {
> + space_info = __find_space_info(fs_info,
> + BTRFS_BLOCK_GROUP_METADATA);
> + }
Could you please convert that to something like that:
u64 flags
if (is_system)
flags = BTRFS_BLOCK_GROUP_SYSTEM;
else if (is_data)
etc
__find_space_info(fs_info, flags);
This is to avoid repeating the same function call.
> + ASSERT(space_info);
> + percpu_counter_add(&space_info->total_bytes_pinned,
> -head->num_bytes);
> - btrfs_put_block_group(cache);
>
> if (head->is_data) {
> spin_lock(&delayed_refs->lock);
> --
> 2.7.4
>
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