https://bugzilla.kernel.org/show_bug.cgi?id=201461 --- Comment #4 from zhenbianshu@xxxxxxxxxxx --- (In reply to Theodore Tso from comment #3) > 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. I did not find ext4_writepages() or mpage_map_one_extent() in linux 3.10.0 source code, what I found is ext4_da_writepages(). And the call chain: journal_submit_data_buffers() journal_submit_inode_data_buffers() generic_writepages() ext4_da_writepages() write_cache_page_da() mpage_da_map_and_submit() ext4_map_blocks() will take the write lock of i_data_sem. Will generic_writepages() call ext4_da_writepages() in jbd2 ? -- You are receiving this mail because: You are watching the assignee of the bug.
