Syzbot reported a BUG_ON: ================================================================== EXT4-fs (loop0): mounted filesystem without journal. Quota mode: none. EXT4-fs error (device loop0): ext4_mb_generate_buddy:1098: group 0, block bitmap and bg descriptor inconsistent: 25 vs 150994969 free clusters ------------[ cut here ]------------ kernel BUG at fs/ext4/ext4_jbd2.c:53! invalid opcode: 0000 [#1] PREEMPT SMP KASAN CPU: 1 PID: 494 Comm: syz-executor.0 6.1.0-rc7-syzkaller-ga4412fdd49dc #0 RIP: 0010:__ext4_journal_stop+0x1b3/0x1c0 [...] Call Trace: ext4_write_inline_data_end+0xa39/0xdf0 ext4_da_write_end+0x1e2/0x950 generic_perform_write+0x401/0x5f0 ext4_buffered_write_iter+0x35f/0x640 ext4_file_write_iter+0x198/0x1cd0 vfs_write+0x8b5/0xef0 [...] ==================================================================
The above BUG_ON is triggered by the following race:
cpu1 cpu2 ________________________|________________________ ksys_write vfs_write new_sync_write ext4_file_write_iter ext4_buffered_write_iter generic_perform_write ext4_da_write_begin do_fault do_page_mkwrite ext4_page_mkwrite ext4_convert_inline_data ext4_convert_inline_data_nolock ext4_destroy_inline_data_nolock //clear EXT4_STATE_MAY_INLINE_DATA ext4_map_blocks --> return error ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) ext4_block_write_begin ext4_restore_inline_data // set EXT4_STATE_MAY_INLINE_DATA ext4_da_write_end ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) ext4_write_inline_data_end handle=NULL ext4_journal_stop(handle) __ext4_journal_stop ext4_put_nojournal(handle) ref_cnt = (unsigned long)handle BUG_ON(ref_cnt == 0) ---> BUG_ON
The root cause of this problem is that the ext4_convert_inline_data() in ext4_page_mkwrite() does not grab i_rwsem, so it may race with ext4_buffered_write_iter() and cause the write_begin() and write_end() functions to be inconsistent and trigger BUG_ON.
To solve the above issue, we cannot add inode_lock directly to ext4_page_mkwrite(), because this function is a hot path and frequent calls to inode_lock will cause performance degradation for multi-threaded reads and writes. Hence, we move ext4_convert_inline_data() to ext4_file_mmap(), and only when inline_data is enabled and mmap a file in shared write mode, we hold the lock to convert, which can reduce the impact on performance.
Reported-by: Jun Nie jun.nie@linaro.org Closes: https://lore.kernel.org/lkml/63903521.5040307@huawei.com/t/ Reported-by: syzbot+a158d886ca08a3fecca4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?id=899b37f20ce4072bcdfecfe1647b39602e956e3... Fixes: 7b4cc9787fe3 ("ext4: evict inline data when writing to memory map") CC: stable@vger.kernel.org # 4.12+ Signed-off-by: Baokun Li libaokun1@huawei.com --- fs/ext4/file.c | 24 +++++++++++++++++++++++- fs/ext4/inode.c | 4 ---- 2 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c index d101b3b0c7da..7a04376c33f2 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -795,7 +795,8 @@ static const struct vm_operations_struct ext4_file_vm_ops = { static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma) { struct inode *inode = file->f_mapping->host; - struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); + struct super_block *sb = inode->i_sb; + struct ext4_sb_info *sbi = EXT4_SB(sb); struct dax_device *dax_dev = sbi->s_daxdev;
if (unlikely(ext4_forced_shutdown(sbi))) @@ -808,6 +809,27 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma) if (!daxdev_mapping_supported(vma, dax_dev)) return -EOPNOTSUPP;
+ /* + * Writing via mmap has no logic to handle inline data, so we + * need to call ext4_convert_inline_data() to convert the inode + * to normal format before doing so, otherwise a BUG_ON will be + * triggered in ext4_writepages() due to the + * EXT4_STATE_MAY_INLINE_DATA flag. Moreover, we need to grab + * i_rwsem during conversion, since clearing and setting the + * inline data flag may race with ext4_buffered_write_iter() + * to trigger a BUG_ON. + */ + if (ext4_has_feature_inline_data(sb) && + vma->vm_flags & VM_SHARED && vma->vm_flags & VM_WRITE) { + int err; + + inode_lock(inode); + err = ext4_convert_inline_data(inode); + inode_unlock(inode); + if (err) + return err; + } + file_accessed(file); if (IS_DAX(file_inode(file))) { vma->vm_ops = &ext4_dax_vm_ops; diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index ce5f21b6c2b3..31844c4ec9fe 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -6043,10 +6043,6 @@ vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
filemap_invalidate_lock_shared(mapping);
- err = ext4_convert_inline_data(inode); - if (err) - goto out_ret; - /* * On data journalling we skip straight to the transaction handle: * there's no delalloc; page truncated will be checked later; the