linux-kernel - Re: [PATCH] genirq: fix irq_desc->depth handling with DEBUG

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Date:	Fri, 22 Aug 2008 08:07:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	linux-kernel@...r.kernel.org,
	David Woodhouse <dwmw2@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] genirq: fix irq_desc->depth handling with DEBUG_SHIRQ


* Anton Vorontsov <avorontsov@...mvista.com> wrote:

> When DEBUG_SHIRQ is selected, a spurious IRQ is issued before
> the setup_irq() initializes the desc->depth. An IRQ handler may
> call disable_irq_nosync(), but then setup_irq() will overwrite
> desc->depth, and upon enable_irq() we'll catch this WARN:
> 
> ------------[ cut here ]------------
> Badness at kernel/irq/manage.c:180
> NIP: c0061ab8 LR: c0061f10 CTR: 00000000
> REGS: cf83be50 TRAP: 0700   Not tainted  (2.6.27-rc3-23450-g74919b0)
> MSR: 00021032 <ME,IR,DR>  CR: 22042022  XER: 20000000
> TASK = cf829100[5] 'events/0' THREAD: cf83a000
> GPR00: c0061f10 cf83bf00 cf829100 c038e674 00000016 00000000 cf83bef8 00000038
> GPR08: c0298910 00000000 c0310d28 cf83a000 00000c9c 1001a1a8 0fffe000 00800000
> GPR16: ffffffff 00000000 007fff00 00000000 007ffeb0 c03320a0 c031095c c0310924
> GPR24: cf8292ec cf807190 cf83a000 00009032 c038e6a4 c038e674 cf99b1cc c038e674
> NIP [c0061ab8] __enable_irq+0x20/0x80
> LR [c0061f10] enable_irq+0x50/0x70
> Call Trace:
> [cf83bf00] [c038e674] irq_desc+0x630/0x9000 (unreliable)
> [cf83bf10] [c0061f10] enable_irq+0x50/0x70
> [cf83bf30] [c01abe94] phy_change+0x68/0x108
> [cf83bf50] [c0046394] run_workqueue+0xc4/0x16c
> [cf83bf90] [c0046834] worker_thread+0x74/0xd4
> [cf83bfd0] [c004ab7c] kthread+0x48/0x84
> [cf83bff0] [c00135e0] kernel_thread+0x44/0x60
> Instruction dump:
> 4e800020 3d20c031 38a94214 4bffffcc 9421fff0 7c0802a6 93e1000c 7c7f1b78
> 90010014 8123001c 2f890000 409e001c <0fe00000> 80010014 83e1000c 38210010
> 
> That trace corresponds to this line:
> WARN(1, KERN_WARNING "Unbalanced enable for IRQ %d\n", irq);
> 
> The patch fixes the problem by moving the SHIRQ code below the
> setup_irq().
> 
> Unfortunately we can't easily move the SHIRQ code inside the
> setup_irq(), since it grabs a spinlock, so to prvent a 'real'
> IRQ from interfere us we should disable that IRQ.
> 
> p.s. The driver in question is drivers/net/phy/phy.c.
> 
> Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>

applied to tip/genirq - thanks Anton.

	Ingo
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