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

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Date:	Fri, 23 Mar 2007 03:11:15 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Mingming Cao <cmm@...ibm.com>, Adrian Bunk <bunk@...sta.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Mariusz Kozlowski <m.kozlowski@...land.pl>,
	Oliver Pinter <oliver.pntr@...il.com>,
	Sid Boyce <g3vbv@...eyonder.co.uk>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [1/6] 2.6.21-rc4: known regressions

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?
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