On 04/24/2015 09:43 AM, Filipe David Manana wrote: > On Fri, Apr 24, 2015 at 2:00 PM, Chris Mason <c...@fb.com> wrote:
>> Can you please bang on this and get a more reliable reproduction? I'll >> take a look. > > Not really that easy to get a more reliable reproducer - just run > fsstress with multiple processes - it already happened twice again > after I sent the previous mail. > From the quick look I had at this, this seems to be the change causing > the problem: > > http://git.kernel.org/cgit/linux/kernel/git/mason/linux-btrfs.git/commit/?h=for-linus-4.1&id=1bbc621ef28462456131c035eaeb5567a1a2a2fe > > Early in btrfs_commit_transaction(), btrfs_start_dirty_block_groups() > is called which ends up calling __btrfs_write_out_cache() for each > dirty block group, which collects all the bitmap entries from the bg's > space cache into a local list while holding the cache's ctl->tree_lock > (to serialize with concurrent allocation requests). > > Then we unlock ctl->tree_lock, do other stuff and later acquire > ctl->tree_lock again and call write_bitmap_entries() to write the > bitmap entries we previously collected. However, while we were doing > the other stuff without holding that lock, allocation requests might > have happened right? - since when we call > btrfs_start_dirty_block_groups() in btrfs_commit_transaction() the > transaction state wasn't yet changed, allowing other tasks to join the > current transaction. If such other task allocates all the remaining > space from a bitmap entry we collected before (because it's still in > the space cache's rbtree), it ends up deleting it and freeing its > ->bitmap member, which results in an invalid memory access (and the > warning on the list corruption) when we later call > write_bitmap_entries() in __btrfs_write_out_cache() - which is what > the second part of the trace I sent says: It's easy to hold the ctl->tree_lock from collection write out, but everyone deleting items is using list_del_init, so it should be fine to take the lock again and run through any items that are left. Here's a replacement incremental that'll cover both cases: diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c index d773f22..657a8ec 100644 --- a/fs/btrfs/free-space-cache.c +++ b/fs/btrfs/free-space-cache.c @@ -1119,18 +1119,21 @@ static int flush_dirty_cache(struct inode *inode) } static void noinline_for_stack -cleanup_write_cache_enospc(struct inode *inode, +cleanup_write_cache_enospc(struct btrfs_free_space_ctl *ctl, + struct inode *inode, struct btrfs_io_ctl *io_ctl, struct extent_state **cached_state, struct list_head *bitmap_list) { struct list_head *pos, *n; + spin_lock(&ctl->tree_lock); list_for_each_safe(pos, n, bitmap_list) { struct btrfs_free_space *entry = list_entry(pos, struct btrfs_free_space, list); list_del_init(&entry->list); } + spin_unlock(&ctl->tree_lock); io_ctl_drop_pages(io_ctl); unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1, cached_state, @@ -1266,8 +1269,8 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode, ret = write_cache_extent_entries(io_ctl, ctl, block_group, &entries, &bitmaps, &bitmap_list); - spin_unlock(&ctl->tree_lock); if (ret) { + spin_unlock(&ctl->tree_lock); mutex_unlock(&ctl->cache_writeout_mutex); goto out_nospc; } @@ -1282,6 +1285,7 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode, */ ret = write_pinned_extent_entries(root, block_group, io_ctl, &entries); if (ret) { + spin_unlock(&ctl->tree_lock); mutex_unlock(&ctl->cache_writeout_mutex); goto out_nospc; } @@ -1291,7 +1295,6 @@ static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode, * locked while doing it because a concurrent trim can be manipulating * or freeing the bitmap. */ - spin_lock(&ctl->tree_lock); ret = write_bitmap_entries(io_ctl, &bitmap_list); spin_unlock(&ctl->tree_lock); mutex_unlock(&ctl->cache_writeout_mutex); @@ -1345,7 +1348,8 @@ out: return ret; out_nospc: - cleanup_write_cache_enospc(inode, io_ctl, &cached_state, &bitmap_list); + cleanup_write_cache_enospc(ctl, inode, io_ctl, + &cached_state, &bitmap_list); if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA)) up_write(&block_group->data_rwsem); -- 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
