On Sat, Feb 16, 2008 at 08:53:34AM +0530, Aneesh Kumar K.V wrote: > On Fri, Feb 15, 2008 at 11:43:04AM -0800, Mingming Cao wrote: > > On Fri, 2008-02-15 at 23:46 +0530, Aneesh Kumar K.V wrote: > > > fallocate blocks are considered as sparse area and read from them should > > > return zero. ext4_ext_get_blocks should return zero for read request. > > > > > > > The patch itself looks harmless, but I still don't see how this could > > fix the problem you described at irc: a write hit a BUG_ON() in > > fs/buffer.c saying the buffer is not mapped. Could you add more details > > here? > > Write will take the below call chain > > ext4_write_begin > block_write_begin > __block_prepare_write > ext4_getblock > ext4_get_blocks_wrap > (1) ext4_ext_get_blocks with create = 0 return allocated > ll_rw_block if buffer not uptodate. > submit_bh > BUG_ON(!buffer_mapped(bh)) > > > ext4_ext_get_blocks at (1) should have returned 0. That would cause > ext4_get_blocks_wrap to again call ext4_ext_get_blocks with create = 1 > and that would have returned us the buffer head which is mapped. This > would also result in splitting the extent to initialized and > uninitialized one. > The change is also needed to get mmap on fallocate space to work. ------------[ cut here ]------------ WARNING: at fs/buffer.c:1680 __block_write_full_page+0x101/0x2f1() Modules linked in: Pid: 2478, comm: mmaptest Not tainted 2.6.25-rc1 #12 [<c0120e84>] warn_on_slowpath+0x41/0x51 [<c0108c00>] ? native_sched_clock+0x2d/0x9f [<c013b44e>] ? __lock_acquire+0xacb/0xb13 [<c013b44e>] ? __lock_acquire+0xacb/0xb13 [<c0180f97>] __block_write_full_page+0x101/0x2f1 [<c01d053f>] ? ext4_get_block+0x0/0xc0 [<c018124f>] block_write_full_page+0xc8/0xd1 [<c01d053f>] ? ext4_get_block+0x0/0xc0 [<c01d1a36>] ext4_ordered_writepage+0xad/0x146 [<c01cec12>] ? bget_one+0x0/0xb [<c014c5dd>] __writepage+0xb/0x25 [<c014cab2>] write_cache_pages+0x180/0x287 [<c014c5d2>] ? __writepage+0x0/0x25 [<c01527d5>] ? __do_fault+0x2e2/0x324 [<c0147889>] ? unlock_page+0x25/0x28 [<c014cbd6>] generic_writepages+0x1d/0x27 [<c014cc0c>] do_writepages+0x2c/0x34 [<c0147fe1>] __filemap_fdatawrite_range+0x5b/0x67 [<c01481ba>] filemap_fdatawrite+0x15/0x17 [<c017ea3d>] do_fsync+0x2c/0x9a [<c017eacb>] __do_fsync+0x20/0x2f [<c017eaf9>] sys_fsync+0xd/0xf [<c0104992>] sysenter_past_esp+0x5f/0xa5 ======================= ---[ end trace 5ba60b430e0af601 ]--- -aneesh - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
