From: Filipe Manana fdmanana@suse.com
commit bbc37d6e475eee8ffa2156ec813efc6bbb43c06d upstream.
If a transaction aborts it can cause a memory leak of the pages array of a block group's io_ctl structure. The following steps explain how that can happen:
1) Transaction N is committing, currently in state TRANS_STATE_UNBLOCKED and it's about to start writing out dirty extent buffers;
2) Transaction N + 1 already started and another task, task A, just called btrfs_commit_transaction() on it;
3) Block group B was dirtied (extents allocated from it) by transaction N + 1, so when task A calls btrfs_start_dirty_block_groups(), at the very beginning of the transaction commit, it starts writeback for the block group's space cache by calling btrfs_write_out_cache(), which allocates the pages array for the block group's io_ctl with a call to io_ctl_init(). Block group A is added to the io_list of transaction N + 1 by btrfs_start_dirty_block_groups();
4) While transaction N's commit is writing out the extent buffers, it gets an IO error and aborts transaction N, also setting the file system to RO mode;
5) Task A has already returned from btrfs_start_dirty_block_groups(), is at btrfs_commit_transaction() and has set transaction N + 1 state to TRANS_STATE_COMMIT_START. Immediately after that it checks that the filesystem was turned to RO mode, due to transaction N's abort, and jumps to the "cleanup_transaction" label. After that we end up at btrfs_cleanup_one_transaction() which calls btrfs_cleanup_dirty_bgs(). That helper finds block group B in the transaction's io_list but it never releases the pages array of the block group's io_ctl, resulting in a memory leak.
In fact at the point when we are at btrfs_cleanup_dirty_bgs(), the pages array points to pages that were already released by us at __btrfs_write_out_cache() through the call to io_ctl_drop_pages(). We end up freeing the pages array only after waiting for the ordered extent to complete through btrfs_wait_cache_io(), which calls io_ctl_free() to do that. But in the transaction abort case we don't wait for the space cache's ordered extent to complete through a call to btrfs_wait_cache_io(), so that's why we end up with a memory leak - we wait for the ordered extent to complete indirectly by shutting down the work queues and waiting for any jobs in them to complete before returning from close_ctree().
We can solve the leak simply by freeing the pages array right after releasing the pages (with the call to io_ctl_drop_pages()) at __btrfs_write_out_cache(), since we will never use it anymore after that and the pages array points to already released pages at that point, which is currently not a problem since no one will use it after that, but not a good practice anyway since it can easily lead to use-after-free issues.
So fix this by freeing the pages array right after releasing the pages at __btrfs_write_out_cache().
This issue can often be reproduced with test case generic/475 from fstests and kmemleak can detect it and reports it with the following trace:
unreferenced object 0xffff9bbf009fa600 (size 512): comm "fsstress", pid 38807, jiffies 4298504428 (age 22.028s) hex dump (first 32 bytes): 00 a0 7c 4d 3d ed ff ff 40 a0 7c 4d 3d ed ff ff ..|M=...@.|M=... 80 a0 7c 4d 3d ed ff ff c0 a0 7c 4d 3d ed ff ff ..|M=.....|M=... backtrace: [<00000000f4b5cfe2>] __kmalloc+0x1a8/0x3e0 [<0000000028665e7f>] io_ctl_init+0xa7/0x120 [btrfs] [<00000000a1f95b2d>] __btrfs_write_out_cache+0x86/0x4a0 [btrfs] [<00000000207ea1b0>] btrfs_write_out_cache+0x7f/0xf0 [btrfs] [<00000000af21f534>] btrfs_start_dirty_block_groups+0x27b/0x580 [btrfs] [<00000000c3c23d44>] btrfs_commit_transaction+0xa6f/0xe70 [btrfs] [<000000009588930c>] create_subvol+0x581/0x9a0 [btrfs] [<000000009ef2fd7f>] btrfs_mksubvol+0x3fb/0x4a0 [btrfs] [<00000000474e5187>] __btrfs_ioctl_snap_create+0x119/0x1a0 [btrfs] [<00000000708ee349>] btrfs_ioctl_snap_create_v2+0xb0/0xf0 [btrfs] [<00000000ea60106f>] btrfs_ioctl+0x12c/0x3130 [btrfs] [<000000005c923d6d>] __x64_sys_ioctl+0x83/0xb0 [<0000000043ace2c9>] do_syscall_64+0x33/0x80 [<00000000904efbce>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
CC: stable@vger.kernel.org # 4.9+ 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: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/disk-io.c | 1 + fs/btrfs/free-space-cache.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-)
--- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -4477,6 +4477,7 @@ static void btrfs_cleanup_bg_io(struct b cache->io_ctl.inode = NULL; iput(inode); } + ASSERT(cache->io_ctl.pages == NULL); btrfs_put_block_group(cache); }
--- a/fs/btrfs/free-space-cache.c +++ b/fs/btrfs/free-space-cache.c @@ -1166,7 +1166,6 @@ static int __btrfs_wait_cache_io(struct ret = update_cache_item(trans, root, inode, path, offset, io_ctl->entries, io_ctl->bitmaps); out: - io_ctl_free(io_ctl); if (ret) { invalidate_inode_pages2(inode->i_mapping); BTRFS_I(inode)->generation = 0; @@ -1329,6 +1328,7 @@ static int __btrfs_write_out_cache(struc * them out later */ io_ctl_drop_pages(io_ctl); + io_ctl_free(io_ctl);
unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1, &cached_state);