Re: [1/6] 2.6.21-rc4: known regressions

Linus Torvalds
2007-03-23T01:47:43Z

[ Ok, I think it's those timers again...

Ingo: let me just state how *happy* I am that I told you off when you
wanted to merge the hires timers and NO_HZ before 2.6.20 because they
were "stable". You were wrong, and 2.6.20 is at least in reasonable
shape. Now we just need to make sure that 2.6.21 will be too.. ]

On Thu, 22 Mar 2007, Mingming Cao wrote:
>
> I might missed something, so far I can't see a deadlock yet.
> If there is a deadlock, I think we should see ext3_xattr_release_block()
> and ext3_forget() on the stack. Is this the case?

No. What's strange is that two (maybe more, I didn't check) processes seem
to be stuck in

[<c0318981>] schedule_timeout+0x70/0x8e
[<c03189b4>] schedule_timeout_uninterruptible+0x15/0x17
[<c01b964a>] journal_stop+0xe2/0x1e6
[<c01ba2b0>] journal_force_commit+0x1d/0x1f
[<c01b29fb>] ext3_force_commit+0x22/0x24
[<c01ad607>] ext3_write_inode+0x34/0x3a
[<c0189f74>] __writeback_single_inode+0x1c5/0x2cb
[<c018a096>] sync_inode+0x1c/0x2e
[<c01a9ff7>] ext3_sync_file+0xab/0xc0
[<c018c8c5>] do_fsync+0x4b/0x98
[<c018c932>] __do_fsync+0x20/0x2f
[<c018c960>] sys_fsync+0xd/0xf
[<c0104064>] syscall_call+0x7/0xb

but that that thing is literally:

...
do {
old_handle_count = transaction->t_handle_count;
schedule_timeout_uninterruptible(1);
} while (old_handle_count != transaction->t_handle_count);
...

and especially if nothing is happening, I'd not expect
"transaction->t_handle_count" to keep changing, so it should stop very
quickly.

Maybe it's CONFIG_NO_HZ again, and the problem is that timeout, and simply
no timer tick happening?

Bingo. I think that's it.

active timers:
#0: hardirq_stack, tick_sched_timer, S:01
# expires at 9530893000000 nsecs [in -2567889 nsecs]
#1: hardirq_stack, hrtimer_wakeup, S:01
# expires at 10858649798503 nsecs [in 1327754230614 nsecs]
.expires_next : 9530893000000 nsecs

See

http://lkml.org/lkml/2007/3/16/288

and that in turn points to the kernel log: