linux-kernel - Re: [2.6.23-rt3] NMI watchdog trace of deadlock

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Message-ID: <20071027094407.GA12047@elte.hu>
Date:	Sat, 27 Oct 2007 11:44:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Mike Galbraith <efault@....de>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [2.6.23-rt3] NMI watchdog trace of deadlock


* Nick Piggin <nickpiggin@...oo.com.au> wrote:

> > [10138.175796]  [<c0105de3>] show_trace+0x12/0x14
> > [10138.180291]  [<c0105dfb>] dump_stack+0x16/0x18
> > [10138.184769]  [<c011609f>] native_smp_call_function_mask+0x138/0x13d
> > [10138.191117]  [<c0117606>] smp_call_function+0x1e/0x24
> > [10138.196210]  [<c012f85c>] on_each_cpu+0x25/0x50
> > [10138.200807]  [<c0115c74>] flush_tlb_all+0x1e/0x20
> > [10138.205553]  [<c016caaf>] kmap_high+0x1b6/0x417
> > [10138.210118]  [<c011ec88>] kmap+0x4d/0x4f
> > [10138.214102]  [<c026a9d8>] ntfs_end_buffer_async_read+0x228/0x2f9
> > [10138.220163]  [<c01a0e9e>] end_bio_bh_io_sync+0x26/0x3f
> > [10138.225352]  [<c01a2b09>] bio_endio+0x42/0x6d
> > [10138.229769]  [<c02c2a08>] __end_that_request_first+0x115/0x4ac
> > [10138.235682]  [<c02c2da7>] end_that_request_chunk+0x8/0xa
> > [10138.241052]  [<c0365943>] ide_end_request+0x55/0x10a
> > [10138.246058]  [<c036dae3>] ide_dma_intr+0x6f/0xac
> > [10138.250727]  [<c0366d83>] ide_intr+0x93/0x1e0
> > [10138.255125]  [<c015afb4>] handle_IRQ_event+0x5c/0xc9
> 
> Looks like ntfs is kmap()ing from interrupt context. Should be using 
> kmap_atomic instead, I think.

it's not atomic interrupt context but irq thread context - and -rt 
remaps kmap_atomic() to kmap() internally.

the problem seems to be what Mike's patch works around: fiddling with 
irq flags in the ntfs code. That fiddling seems quite unnecessary at 
first sight.

	Ingo
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