From: Eric Sandeen Date: Sat, 29 Oct 2011 14:15:35 +0000 (-0400) Subject: ext4: fix race in xattr block allocation path X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=6d6a435190bdf2e04c9465cde5bdc3ac68cf11a4;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git ext4: fix race in xattr block allocation path Ceph users reported that when using Ceph on ext4, the filesystem would often become corrupted, containing inodes with incorrect i_blocks counters. I managed to reproduce this with a very hacked-up "streamtest" binary from the Ceph tree. Ceph is doing a lot of xattr writes, to out-of-inode blocks. There is also another thread which does sync_file_range and close, of the same files. The problem appears to happen due to this race: sync/flush thread xattr-set thread ----------------- ---------------- do_writepages ext4_xattr_set ext4_da_writepages ext4_xattr_set_handle mpage_da_map_blocks ext4_xattr_block_set set DELALLOC_RESERVE ext4_new_meta_blocks ext4_mb_new_blocks if (!i_delalloc_reserved_flag) vfs_dq_alloc_block ext4_get_blocks down_write(i_data_sem) set i_delalloc_reserved_flag ... up_write(i_data_sem) if (i_delalloc_reserved_flag) vfs_dq_alloc_block_nofail In other words, the sync/flush thread pops in and sets i_delalloc_reserved_flag on the inode, which makes the xattr thread think that it's in a delalloc path in ext4_new_meta_blocks(), and add the block for a second time, after already having added it once in the !i_delalloc_reserved_flag case in ext4_mb_new_blocks The real problem is that we shouldn't be using the DELALLOC_RESERVED state flag, and instead we should be passing EXT4_GET_BLOCKS_DELALLOC_RESERVE down to ext4_map_blocks() instead of using an inode state flag. We'll fix this for now with using i_data_sem to prevent this race, but this is really not the right way to fix things. Signed-off-by: Eric Sandeen Signed-off-by: "Theodore Ts'o" Cc: stable@kernel.org --- diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index 0ae3668520f8..93a00d89a220 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -820,8 +820,14 @@ inserted: if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) goal = goal & EXT4_MAX_BLOCK_FILE_PHYS; + /* + * take i_data_sem because we will test + * i_delalloc_reserved_flag in ext4_mb_new_blocks + */ + down_read((&EXT4_I(inode)->i_data_sem)); block = ext4_new_meta_blocks(handle, inode, goal, 0, NULL, &error); + up_read((&EXT4_I(inode)->i_data_sem)); if (error) goto cleanup;