https://bugzilla.kernel.org/show_bug.cgi?id=201461 --- Comment #3 from Theodore Tso (tytso@xxxxxxx) --- The writeback code will end up calling ext4_writepages(), which will do block allocations via ext4_map_blocks() with the flag EXT4_GET_BLOCKS_CREATE(), and this will take a write lock on i_data_sem. I'll let you trace through the call chain that starts in the writeback thread, through the call to ext4_writepages(), proceeds to mpage_map_one_extent(), and from there to ext4_map_blocks() which actually holds the write block. Note that this is distinct from the data=ordered forced writeblock which starts in fs/jbd2's journal_submit_inode_data_buffer() calling generic_writepages(). The difference is that generic_writepages() will only call writepage() function. For ext4 that's ext4_writepage(), which will never do block allocation. But the writeback threads call the address space operation's, writepages() function, and ext4_writepages() *will* do block allocation for delayed allocation writes. This is a subtle point; ext4_writepage() and ext4_writepages() do very different things. The first is used by the commit kernel thread; the second is used by the writeback kernel thread. -- You are receiving this mail because: You are watching the assignee of the bug.
