Re: [PATCH v1 0/9] do not use s_dirt in ext4

On Tue, 2012-03-27 at 22:14 +0200, Jan Kara wrote:

On Tue 27-03-12 16:29:58, Artem Bityutskiy wrote:

quoted

On Thu, 2012-03-22 at 11:33 +0100, Jan Kara wrote:

quoted

  Then we have ext4_mark_super_dirty() call from 4 places - I forgot about
these originally... I kind of miss their purpose. Originally they were used
so that we write total number of free blocks and inodes in the superblock
but when we do not maintain them in the journal mode I don't see a reason
to periodically sync them in no-journal mode. Ted, what is the purpose of
these calls?

I do not understand what's the fundamental difference between journal
and non-journal mode. Why when we do have the journal we do not mark the
super-block as dirty in many places (e.g., in 'ext4_file_open()' - if we
do have the journal, when do we make sure we save the mount point path
change?).

  We write it at least during ext4_put_super().

quoted

May be it has something to do with behaving like the ext2 driver when
mounting ext2-formatted media with the the ext4 driver?

  I'm not really sure about this...

quoted

Jan, since Ted did not answer, may be you can figure out the reasons
from this commit message, which actually introduced the
'ext4_mark_super_dirty()' function?

  Anyway, attached are two patches which you can include in your series
and which should make your cleanups simpler.

I amended the second patch:
-                               ext4_journal_stop(sb);
+                               ext4_journal_stop(sbi->s_sbh);

Extensive testing with xfstests found a problem with these patches:

[23500.238579] ------------[ cut here ]------------
[23500.238720] kernel BUG at fs/buffer.c:2871!
[23500.238842] invalid opcode: 0000 [#1] SMP 
[23500.239279] CPU 11 
[23500.239338] Modules linked in: [last unloaded: scsi_wait_scan]
[23500.239442] 
[23500.239442] Pid: 15799, comm: fsstress Not tainted 3.3.0+ #43 Bochs Bochs
[23500.239442] RIP: 0010:[<ffffffff811a9add>]  [<ffffffff811a9add>] submit_bh+0x10d/0x120
[23500.239442] RSP: 0018:ffff880273a41b58  EFLAGS: 00010202
[23500.239442] RAX: 000000000004d025 RBX: ffff8802469e5a90 RCX: 0000000000000000
[23500.239442] RDX: ffff880273a41fd8 RSI: ffff8802469e5a90 RDI: 0000000000000211
[23500.239442] RBP: ffff880273a41b78 R08: ffff880409645d80 R09: 0000000000000001
[23500.239442] R10: 0000000000000001 R11: ffff880178439000 R12: 0000000000000211
[23500.239442] R13: ffff880273a41c34 R14: ffff8804059b7000 R15: ffff880273a41fd8
[23500.239442] FS:  00007fc8731e7700(0000) GS:ffff88041fd60000(0000) knlGS:0000000000000000
[23500.239442] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[23500.239442] CR2: 00007fc873082008 CR3: 000000012456a000 CR4: 00000000000006e0
[23500.239442] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[23500.239442] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[23500.239442] Process fsstress (pid: 15799, threadinfo ffff880273a40000, task ffff880150dd8000)
[23500.239442] Stack:
[23500.239442]  ffff8804059b7000 ffff8802469e5a90 0000000000000211 ffff880273a41c34
[23500.239442]  ffff880273a41b98 ffffffff811ab59d 0000000000000002 ffff8804059b7128
[23500.239442]  ffff880273a41bf8 ffffffff8123be1d 0000000091827364 ffff88010e9a7e30
[23500.239442] Call Trace:
[23500.239442]  [<ffffffff811ab59d>] write_dirty_buffer+0x4d/0x80
[23500.239442]  [<ffffffff8123be1d>] __flush_batch+0x4d/0xa0
[23500.239442]  [<ffffffff8123c605>] jbd2_log_do_checkpoint+0xf5/0x4f0
[23500.239442]  [<ffffffff8123ca89>] __jbd2_log_wait_for_space+0x89/0x190
[23500.239442]  [<ffffffff81237a98>] start_this_handle+0x3a8/0x4e0
[23500.239442]  [<ffffffff810799e0>] ? remove_wait_queue+0x50/0x50
[23500.239442]  [<ffffffff81237c93>] jbd2__journal_start+0xc3/0x100
[23500.239442]  [<ffffffff81237ce3>] jbd2_journal_start+0x13/0x20
[23500.239442]  [<ffffffff8121743f>] ext4_journal_start_sb+0x7f/0x1d0
[23500.239442]  [<ffffffff81224a24>] ? ext4_fallocate+0x1a4/0x530
[23500.239442]  [<ffffffff811f64c5>] ? ext4_meta_trans_blocks+0xa5/0xb0
[23500.239442]  [<ffffffff81224a24>] ext4_fallocate+0x1a4/0x530
[23500.239442]  [<ffffffff8117a092>] do_fallocate+0xf2/0x160
[23500.239442]  [<ffffffff8117a14b>] sys_fallocate+0x4b/0x70
[23500.239442]  [<ffffffff815e6d69>] system_call_fastpath+0x16/0x1b
[23500.239442] Code: ee 44 89 e7 e8 35 1f 0f 00 49 8b 5d 18 4c 89 ef e8 19 4e 00 00 48 83 c4 08 c1 e3 18 c1 fb 1f 83 e3 a1 89 d8 5b 41 5c 41 5d 5d c3 <0f> 0b 0f 0b 0f 0b 0f 0b 0f 0b 66 0f 1f 84 00 00 00 00 00 55 48 
[23500.239442] RIP  [<ffffffff811a9add>] submit_bh+0x10d/0x120
[23500.239442]  RSP <ffff880273a41b58>
[23500.261657] ---[ end trace 3db7a7a7ae953551 ]---
[23500.262131] ------------[ cut here ]------------
[23500.262577] WARNING: at kernel/exit.c:897 do_exit+0x55/0x870()
[23500.263070] Hardware name: Bochs
[23500.263467] Modules linked in: [last unloaded: scsi_wait_scan]
[23500.264129] Pid: 15799, comm: fsstress Tainted: G      D      3.3.0+ #43
[23500.264623] Call Trace:
[23500.265066]  [<ffffffff810572bf>] warn_slowpath_common+0x7f/0xc0
[23500.265542]  [<ffffffff8105731a>] warn_slowpath_null+0x1a/0x20
[23500.266034]  [<ffffffff8105b1c5>] do_exit+0x55/0x870
[23500.266482]  [<ffffffff81058f6c>] ? kmsg_dump+0x5c/0xf0
[23500.266932]  [<ffffffff815dfeac>] oops_end+0xac/0xf0
[23500.267418]  [<ffffffff81017928>] die+0x58/0x90
[23500.267852]  [<ffffffff815df7a4>] do_trap+0xc4/0x170
[23500.268343]  [<ffffffff81014fa5>] do_invalid_op+0x95/0xb0
[23500.268803]  [<ffffffff811a9add>] ? submit_bh+0x10d/0x120
[23500.269344]  [<ffffffff81299db4>] ? drive_stat_acct+0x114/0x190
[23500.269825]  [<ffffffff8129ec36>] ? blk_queue_bio+0x106/0x400
[23500.270324]  [<ffffffff815e7f9b>] invalid_op+0x1b/0x20
[23500.270778]  [<ffffffff811a9add>] ? submit_bh+0x10d/0x120
[23500.271263]  [<ffffffff811a9ac7>] ? submit_bh+0xf7/0x120
[23500.271723]  [<ffffffff811ab59d>] write_dirty_buffer+0x4d/0x80
[23500.272217]  [<ffffffff8123be1d>] __flush_batch+0x4d/0xa0
[23500.272675]  [<ffffffff8123c605>] jbd2_log_do_checkpoint+0xf5/0x4f0
[23500.273226]  [<ffffffff8123ca89>] __jbd2_log_wait_for_space+0x89/0x190
[23500.273714]  [<ffffffff81237a98>] start_this_handle+0x3a8/0x4e0
[23500.274213]  [<ffffffff810799e0>] ? remove_wait_queue+0x50/0x50
[23500.274686]  [<ffffffff81237c93>] jbd2__journal_start+0xc3/0x100
[23500.275193]  [<ffffffff81237ce3>] jbd2_journal_start+0x13/0x20
[23500.275664]  [<ffffffff8121743f>] ext4_journal_start_sb+0x7f/0x1d0
[23500.276166]  [<ffffffff81224a24>] ? ext4_fallocate+0x1a4/0x530
[23500.276638]  [<ffffffff811f64c5>] ? ext4_meta_trans_blocks+0xa5/0xb0
[23500.277186]  [<ffffffff81224a24>] ext4_fallocate+0x1a4/0x530
[23500.277654]  [<ffffffff8117a092>] do_fallocate+0xf2/0x160
[23500.278164]  [<ffffffff8117a14b>] sys_fallocate+0x4b/0x70
[23500.278624]  [<ffffffff815e6d69>] system_call_fastpath+0x16/0x1b
[23500.279124] ---[ end trace 3db7a7a7ae953552 ]---

-- 
Best Regards,
Artem Bityutskiy