On Mon, Jan 14, 2013 at 03:50:31PM +0800, Miao Xie wrote: > On thu, 10 Jan 2013 18:57:35 +0100, David Sterba wrote: > > On Thu, Jan 10, 2013 at 08:51:59PM +0800, Miao Xie wrote: > >> There is no lock to protect fs_info->fs_state, it will introduce some > >> problems, > >> such as the value may be covered by the other task when several tasks > >> modify > >> it. Now we use bit operation for it to fix the above problem. > > > > Can you please describe in more detail how does that happen and to what > > problems it leads? > > For example: > Task0 - CPU0 Task1 - CPU1 > mov %fs_state rax > or $0x1 rax > mov %fs_state rax > or $0x2 rax > mov rax %fs_state > mov rax %fs_state > > The expected value is 3, but in fact, it is 2
The code shows that fs_state is only set by open_ctree() and save_error_info(), how could the above race can happen? Although I'm ok with this as a harmless cleanup patch, I'm afraid the commit log is not persuadable anyway. thanks, liubo > > Thanks > Miao > > > > > thanks, > > david > > > >> Signed-off-by: Miao Xie <mi...@cn.fujitsu.com> > >> --- > >> fs/btrfs/ctree.h | 4 +++- > >> fs/btrfs/disk-io.c | 5 +++-- > >> fs/btrfs/file.c | 2 +- > >> fs/btrfs/scrub.c | 2 +- > >> fs/btrfs/super.c | 4 ++-- > >> fs/btrfs/transaction.c | 9 ++++----- > >> 6 files changed, 14 insertions(+), 12 deletions(-) > >> > >> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > >> index c95b539..c34e36e 100644 > >> --- a/fs/btrfs/ctree.h > >> +++ b/fs/btrfs/ctree.h > >> @@ -338,7 +338,9 @@ static inline unsigned long btrfs_chunk_item_size(int > >> num_stripes) > >> /* > >> * File system states > >> */ > >> +#define BTRFS_FS_STATE_ERROR 0 > >> > >> +/* Super block flags */ > >> /* Errors detected */ > >> #define BTRFS_SUPER_FLAG_ERROR (1ULL << 2) > >> > >> @@ -1540,7 +1542,7 @@ struct btrfs_fs_info { > >> u64 qgroup_seq; > >> > >> /* filesystem state */ > >> - u64 fs_state; > >> + unsigned long fs_state; > >> > >> struct btrfs_delayed_root *delayed_root; > >> > >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > >> index cf03a45..d06e50c 100644 > >> --- a/fs/btrfs/disk-io.c > >> +++ b/fs/btrfs/disk-io.c > >> @@ -2196,7 +2196,8 @@ int open_ctree(struct super_block *sb, > >> goto fail_alloc; > >> > >> /* check FS state, whether FS is broken. */ > >> - fs_info->fs_state |= btrfs_super_flags(disk_super); > >> + if (btrfs_super_flags(disk_super) & BTRFS_SUPER_FLAG_ERROR) > >> + set_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state); > >> > >> ret = btrfs_check_super_valid(fs_info, sb->s_flags & MS_RDONLY); > >> if (ret) { > >> @@ -3354,7 +3355,7 @@ int close_ctree(struct btrfs_root *root) > >> printk(KERN_ERR "btrfs: commit super ret %d\n", ret); > >> } > >> > >> - if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) > >> + if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) > >> btrfs_error_commit_super(root); > >> > >> btrfs_put_block_group_cache(fs_info); > >> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > >> index 3e9fa0e..ec87b69 100644 > >> --- a/fs/btrfs/file.c > >> +++ b/fs/btrfs/file.c > >> @@ -1531,7 +1531,7 @@ static ssize_t btrfs_file_aio_write(struct kiocb > >> *iocb, > >> * although we have opened a file as writable, we have > >> * to stop this write operation to ensure FS consistency. > >> */ > >> - if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) { > >> + if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state)) { > >> mutex_unlock(&inode->i_mutex); > >> err = -EROFS; > >> goto out; > >> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c > >> index af0b566..2e91b56 100644 > >> --- a/fs/btrfs/scrub.c > >> +++ b/fs/btrfs/scrub.c > >> @@ -2700,7 +2700,7 @@ static noinline_for_stack int scrub_supers(struct > >> scrub_ctx *sctx, > >> int ret; > >> struct btrfs_root *root = sctx->dev_root; > >> > >> - if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) > >> + if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state)) > >> return -EIO; > >> > >> gen = atomic64_read(&root->fs_info->last_trans_committed); > >> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c > >> index 6f0524d..f714379 100644 > >> --- a/fs/btrfs/super.c > >> +++ b/fs/btrfs/super.c > >> @@ -98,7 +98,7 @@ static void __save_error_info(struct btrfs_fs_info > >> *fs_info) > >> * today we only save the error info into ram. Long term we'll > >> * also send it down to the disk > >> */ > >> - fs_info->fs_state = BTRFS_SUPER_FLAG_ERROR; > >> + set_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state); > >> } > >> > >> static void save_error_info(struct btrfs_fs_info *fs_info) > >> @@ -114,7 +114,7 @@ static void btrfs_handle_error(struct btrfs_fs_info > >> *fs_info) > >> if (sb->s_flags & MS_RDONLY) > >> return; > >> > >> - if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) { > >> + if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) { > >> sb->s_flags |= MS_RDONLY; > >> printk(KERN_INFO "btrfs is forced readonly\n"); > >> /* > >> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c > >> index 7999bf8..a950d48 100644 > >> --- a/fs/btrfs/transaction.c > >> +++ b/fs/btrfs/transaction.c > >> @@ -62,7 +62,7 @@ static noinline int join_transaction(struct btrfs_root > >> *root, int type) > >> spin_lock(&fs_info->trans_lock); > >> loop: > >> /* The file system has been taken offline. No new transactions. */ > >> - if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) { > >> + if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) { > >> spin_unlock(&fs_info->trans_lock); > >> return -EROFS; > >> } > >> @@ -114,7 +114,7 @@ loop: > >> kmem_cache_free(btrfs_transaction_cachep, cur_trans); > >> cur_trans = fs_info->running_transaction; > >> goto loop; > >> - } else if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) { > >> + } else if (test_bit(BTRFS_FS_STATE_ERROR, &fs_info->fs_state)) { > >> spin_unlock(&fs_info->trans_lock); > >> kmem_cache_free(btrfs_transaction_cachep, cur_trans); > >> return -EROFS; > >> @@ -302,7 +302,7 @@ start_transaction(struct btrfs_root *root, u64 > >> num_items, int type, > >> int ret; > >> u64 qgroup_reserved = 0; > >> > >> - if (root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) > >> + if (test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state)) > >> return ERR_PTR(-EROFS); > >> > >> if (current->journal_info) { > >> @@ -635,9 +635,8 @@ static int __btrfs_end_transaction(struct > >> btrfs_trans_handle *trans, > >> btrfs_run_delayed_iputs(root); > >> > >> if (trans->aborted || > >> - root->fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) { > >> + test_bit(BTRFS_FS_STATE_ERROR, &root->fs_info->fs_state)) > >> err = -EIO; > >> - } > >> assert_qgroups_uptodate(trans); > >> > >> memset(trans, 0, sizeof(*trans)); > >> -- > >> 1.7.11.7 > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > >> the body of a message to majord...@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > the body of a message to majord...@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html