Subject: Re: 2.6.35-rc2-git2: Reported regressions from 2.6.34

From: Ingo Molnar <[email-masked]>
Date: Wed, 9 Jun 2010 11:32:49 +0200

* Jens Axboe <[email-masked]> wrote:

> On 2010-06-09 03:53, Linus Torvalds wrote:
> >> Bug-Entry	: http://bugzilla.kernel.org/show_bug.cgi?id=16129
> >> Subject	: BUG: using smp_processor_id() in preemptible [00000000] code: jbd2/sda2
> >> Submitter	: Jan Kreuzer <[email-masked]>
> >> Date		: 2010-06-05 06:15 (4 days old)
> > 
> > This seems to have been introduced by
> > 
> > 	commit 7cbaef9c83e58bbd4bdd534b09052b6c5ec457d5
> > 	Author: Ingo Molnar <[email-masked]>
> > 	Date:   Sat Nov 8 17:05:38 2008 +0100
> > 
> > 	    sched: optimize sched_clock() a bit
> >     
> > 	    sched_clock() uses cycles_2_ns() needlessly - which is an irq-disabling
> > 	    variant of __cycles_2_ns().
> >     
> > 	    Most of the time sched_clock() is called with irqs disabled already.
> > 	    The few places that call it with irqs enabled need to be updated.
> >     
> > 	    Signed-off-by: Ingo Molnar <[email-masked]>
> > 
> > and this seems to be one of those calling cases that need to be updated.
> > 
> > Ingo? The call trace is:
> > 
> > 	BUG: using smp_processor_id() in preemptible [00000000] code: jbd2/sda2-8/337
> > 	caller is native_sched_clock+0x3c/0x68
> > 	Pid: 337, comm: jbd2/sda2-8 Not tainted 2.6.35-rc1jan+ #4
> > 	Call Trace:
> > 	[<ffffffff812362c5>] debug_smp_processor_id+0xc9/0xe4
> > 	[<ffffffff8101059d>] native_sched_clock+0x3c/0x68
> > 	[<ffffffff8101043d>] sched_clock+0x9/0xd
> > 	[<ffffffff81212d7a>] blk_rq_init+0x97/0xa3
> > 	[<ffffffff81214d71>] get_request+0x1c4/0x2d0
> > 	[<ffffffff81214ea6>] get_request_wait+0x29/0x1a6
> > 	[<ffffffff81215537>] __make_request+0x338/0x45b
> > 	[<ffffffff812147c2>] generic_make_request+0x2bb/0x330
> > 	[<ffffffff81214909>] submit_bio+0xd2/0xef
> > 	[<ffffffff811413cb>] submit_bh+0xf4/0x116
> > 	[<ffffffff81144853>] block_write_full_page_endio+0x89/0x96
> > 	[<ffffffff81144875>] block_write_full_page+0x15/0x17
> > 	[<ffffffff8119b00a>] ext4_writepage+0x356/0x36b
> > 	[<ffffffff810e1f91>] __writepage+0x1a/0x39
> > 	[<ffffffff810e32a6>] write_cache_pages+0x20d/0x346
> > 	[<ffffffff810e3406>] generic_writepages+0x27/0x29
> > 	[<ffffffff811ca279>] journal_submit_data_buffers+0x110/0x17d
> > 	[<ffffffff811ca986>] jbd2_journal_commit_transaction+0x4cb/0x156d
> > 	[<ffffffff811d0cba>] kjournald2+0x147/0x37a
> > 
> > (from the bugzilla thing)
> 
> This should be fixed by commit 28f4197e which was merged on friday.

The scheduler commit adding local_clock() (for .36) is:

  c676329: sched_clock: Add local_clock() API and improve documentation

So once that is upstream the block IO statistics code can use that.

Thanks,

	Ingo