From: Filipe Manana fdmanana@suse.com
[ Upstream commit ca84529a842f3a15a5f17beac6252aa11955923f ]
KCSAN complains about a data race when accessing the last_trans field of a root:
[ 199.553628] BUG: KCSAN: data-race in btrfs_record_root_in_trans [btrfs] / record_root_in_trans [btrfs]
[ 199.555186] read to 0x000000008801e308 of 8 bytes by task 2812 on cpu 1: [ 199.555210] btrfs_record_root_in_trans+0x9a/0x128 [btrfs] [ 199.555999] start_transaction+0x154/0xcd8 [btrfs] [ 199.556780] btrfs_join_transaction+0x44/0x60 [btrfs] [ 199.557559] btrfs_dirty_inode+0x9c/0x140 [btrfs] [ 199.558339] btrfs_update_time+0x8c/0xb0 [btrfs] [ 199.559123] touch_atime+0x16c/0x1e0 [ 199.559151] pipe_read+0x6a8/0x7d0 [ 199.559179] vfs_read+0x466/0x498 [ 199.559204] ksys_read+0x108/0x150 [ 199.559230] __s390x_sys_read+0x68/0x88 [ 199.559257] do_syscall+0x1c6/0x210 [ 199.559286] __do_syscall+0xc8/0xf0 [ 199.559318] system_call+0x70/0x98
[ 199.559431] write to 0x000000008801e308 of 8 bytes by task 2808 on cpu 0: [ 199.559464] record_root_in_trans+0x196/0x228 [btrfs] [ 199.560236] btrfs_record_root_in_trans+0xfe/0x128 [btrfs] [ 199.561097] start_transaction+0x154/0xcd8 [btrfs] [ 199.561927] btrfs_join_transaction+0x44/0x60 [btrfs] [ 199.562700] btrfs_dirty_inode+0x9c/0x140 [btrfs] [ 199.563493] btrfs_update_time+0x8c/0xb0 [btrfs] [ 199.564277] file_update_time+0xb8/0xf0 [ 199.564301] pipe_write+0x8ac/0xab8 [ 199.564326] vfs_write+0x33c/0x588 [ 199.564349] ksys_write+0x108/0x150 [ 199.564372] __s390x_sys_write+0x68/0x88 [ 199.564397] do_syscall+0x1c6/0x210 [ 199.564424] __do_syscall+0xc8/0xf0 [ 199.564452] system_call+0x70/0x98
This is because we update and read last_trans concurrently without any type of synchronization. This should be generally harmless and in the worst case it can make us do extra locking (btrfs_record_root_in_trans()) trigger some warnings at ctree.c or do extra work during relocation - this would probably only happen in case of load or store tearing.
So fix this by always reading and updating the field using READ_ONCE() and WRITE_ONCE(), this silences KCSAN and prevents load and store tearing.
Reviewed-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/ctree.c | 4 ++-- fs/btrfs/ctree.h | 10 ++++++++++ fs/btrfs/defrag.c | 2 +- fs/btrfs/disk-io.c | 4 ++-- fs/btrfs/relocation.c | 8 ++++---- fs/btrfs/transaction.c | 8 ++++---- 6 files changed, 23 insertions(+), 13 deletions(-)
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index ca372068226d5..8a791b648ac53 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -321,7 +321,7 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans, WARN_ON(test_bit(BTRFS_ROOT_SHAREABLE, &root->state) && trans->transid != fs_info->running_transaction->transid); WARN_ON(test_bit(BTRFS_ROOT_SHAREABLE, &root->state) && - trans->transid != root->last_trans); + trans->transid != btrfs_get_root_last_trans(root));
level = btrfs_header_level(buf); if (level == 0) @@ -551,7 +551,7 @@ int btrfs_force_cow_block(struct btrfs_trans_handle *trans, WARN_ON(test_bit(BTRFS_ROOT_SHAREABLE, &root->state) && trans->transid != fs_info->running_transaction->transid); WARN_ON(test_bit(BTRFS_ROOT_SHAREABLE, &root->state) && - trans->transid != root->last_trans); + trans->transid != btrfs_get_root_last_trans(root));
level = btrfs_header_level(buf);
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index c03c58246033b..b2e4b30b8fae9 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -354,6 +354,16 @@ static inline void btrfs_set_root_last_log_commit(struct btrfs_root *root, int c WRITE_ONCE(root->last_log_commit, commit_id); }
+static inline u64 btrfs_get_root_last_trans(const struct btrfs_root *root) +{ + return READ_ONCE(root->last_trans); +} + +static inline void btrfs_set_root_last_trans(struct btrfs_root *root, u64 transid) +{ + WRITE_ONCE(root->last_trans, transid); +} + /* * Structure that conveys information about an extent that is going to replace * all the extents in a file range. diff --git a/fs/btrfs/defrag.c b/fs/btrfs/defrag.c index 407ccec3e57ed..f664678c71d15 100644 --- a/fs/btrfs/defrag.c +++ b/fs/btrfs/defrag.c @@ -139,7 +139,7 @@ int btrfs_add_inode_defrag(struct btrfs_trans_handle *trans, if (trans) transid = trans->transid; else - transid = inode->root->last_trans; + transid = btrfs_get_root_last_trans(root);
defrag = kmem_cache_zalloc(btrfs_inode_defrag_cachep, GFP_NOFS); if (!defrag) diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index cabb558dbdaa8..3791813dc7b62 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -658,7 +658,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info, root->state = 0; RB_CLEAR_NODE(&root->rb_node);
- root->last_trans = 0; + btrfs_set_root_last_trans(root, 0); root->free_objectid = 0; root->nr_delalloc_inodes = 0; root->nr_ordered_extents = 0; @@ -1010,7 +1010,7 @@ int btrfs_add_log_tree(struct btrfs_trans_handle *trans, return ret; }
- log_root->last_trans = trans->transid; + btrfs_set_root_last_trans(log_root, trans->transid); log_root->root_key.offset = btrfs_root_id(root);
inode_item = &log_root->root_item.inode; diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c index 8b24bb5a0aa18..f2935252b981a 100644 --- a/fs/btrfs/relocation.c +++ b/fs/btrfs/relocation.c @@ -817,7 +817,7 @@ static struct btrfs_root *create_reloc_root(struct btrfs_trans_handle *trans, goto abort; } set_bit(BTRFS_ROOT_SHAREABLE, &reloc_root->state); - reloc_root->last_trans = trans->transid; + btrfs_set_root_last_trans(reloc_root, trans->transid); return reloc_root; fail: kfree(root_item); @@ -864,7 +864,7 @@ int btrfs_init_reloc_root(struct btrfs_trans_handle *trans, */ if (root->reloc_root) { reloc_root = root->reloc_root; - reloc_root->last_trans = trans->transid; + btrfs_set_root_last_trans(reloc_root, trans->transid); return 0; }
@@ -1739,7 +1739,7 @@ static noinline_for_stack int merge_reloc_root(struct reloc_control *rc, * btrfs_update_reloc_root() and update our root item * appropriately. */ - reloc_root->last_trans = trans->transid; + btrfs_set_root_last_trans(reloc_root, trans->transid); trans->block_rsv = rc->block_rsv;
replaced = 0; @@ -2082,7 +2082,7 @@ static int record_reloc_root_in_trans(struct btrfs_trans_handle *trans, struct btrfs_root *root; int ret;
- if (reloc_root->last_trans == trans->transid) + if (btrfs_get_root_last_trans(reloc_root) == trans->transid) return 0;
root = btrfs_get_fs_root(fs_info, reloc_root->root_key.offset, false); diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 3388c836b9a56..76117bb2c726c 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -405,7 +405,7 @@ static int record_root_in_trans(struct btrfs_trans_handle *trans, int ret = 0;
if ((test_bit(BTRFS_ROOT_SHAREABLE, &root->state) && - root->last_trans < trans->transid) || force) { + btrfs_get_root_last_trans(root) < trans->transid) || force) { WARN_ON(!force && root->commit_root != root->node);
/* @@ -421,7 +421,7 @@ static int record_root_in_trans(struct btrfs_trans_handle *trans, smp_wmb();
spin_lock(&fs_info->fs_roots_radix_lock); - if (root->last_trans == trans->transid && !force) { + if (btrfs_get_root_last_trans(root) == trans->transid && !force) { spin_unlock(&fs_info->fs_roots_radix_lock); return 0; } @@ -429,7 +429,7 @@ static int record_root_in_trans(struct btrfs_trans_handle *trans, (unsigned long)btrfs_root_id(root), BTRFS_ROOT_TRANS_TAG); spin_unlock(&fs_info->fs_roots_radix_lock); - root->last_trans = trans->transid; + btrfs_set_root_last_trans(root, trans->transid);
/* this is pretty tricky. We don't want to * take the relocation lock in btrfs_record_root_in_trans @@ -491,7 +491,7 @@ int btrfs_record_root_in_trans(struct btrfs_trans_handle *trans, * and barriers */ smp_rmb(); - if (root->last_trans == trans->transid && + if (btrfs_get_root_last_trans(root) == trans->transid && !test_bit(BTRFS_ROOT_IN_TRANS_SETUP, &root->state)) return 0;