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

Nick Piggin
2007-03-23T02:11:43Z

On Thu, Mar 22, 2007 at 06:40:41PM -0700, Linus Torvalds wrote:
>
> [ 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:
>
> http://www.stardust.webpages.pl/files/tbf/bitis-gabonica/2.6.21-rc4/git-console.log

Seems convincing. Michal, can you post your .config, and if you had
dynticks and hrtimers enabled, try reproducing without them?