linux-kernel - Re: 2.6.24-git: kmap_atomic() WARN

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Date:	Mon, 25 Feb 2008 20:59:24 +0100
From:	Björn Steinbrink <B.Steinbrink@....de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jeff Garzik <jgarzik@...ox.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.24-git: kmap_atomic() WARN_ON()

On 2008.02.07 00:58:42 +0100, Thomas Gleixner wrote:
> current mainline triggers:
> 
> WARNING: at /home/tglx/work/kernel/x86/linux-2.6/arch/x86/mm/highmem_32.c:52 kmap_atomic_prot+0xe5/0x19b()
> Modules linked in: ahci(+) sata_sil libata sd_mod scsi_mod raid1 ext3 jbd ehci_hcd ohci_hcd uhci_hcd
> Pid: 0, comm: swapper Not tainted 2.6.24 #173
>  [<c0126b60>] warn_on_slowpath+0x41/0x51
>  [<c011c5eb>] ? __enqueue_entity+0x9c/0xa4
>  [<c011c717>] ? enqueue_entity+0x124/0x13b
>  [<c011cedb>] ? enqueue_task_fair+0x41/0x4c
>  [<c032ce88>] ? _spin_lock_irqsave+0x14/0x2e
>  [<c012e885>] ? lock_timer_base+0x1f/0x3e
>  [<c011ad6d>] kmap_atomic_prot+0xe5/0x19b
>  [<c011ae37>] kmap_atomic+0x14/0x16
>  [<f88ea218>] ata_scsi_rbuf_get+0x1e/0x2c [libata]
>  [<f88ea821>] atapi_qc_complete+0x23f/0x289 [libata]
>  [<f88e3d00>] __ata_qc_complete+0x8e/0x93 [libata]
>  [<f88e3fc7>] ata_qc_complete+0x115/0x128 [libata]
>  [<f88e8d47>] ata_qc_complete_multiple+0x86/0xa0 [libata]
>  [<f8841a5d>] ahci_interrupt+0x370/0x40d [ahci]
>  [<c01512c6>] handle_IRQ_event+0x21/0x48
>  [<c01521ca>] handle_edge_irq+0xc9/0x10a
>  [<c0152101>] ? handle_edge_irq+0x0/0x10a
>  [<c0107518>] do_IRQ+0x8b/0xb7
>  [<c01055db>] common_interrupt+0x23/0x28
>  [<c032007b>] ? init_chipset_cmd64x+0xb/0x93
>  [<c010316e>] ? mwait_idle_with_hints+0x39/0x3d
>  [<c0103172>] ? mwait_idle+0x0/0xf
>  [<c010317f>] mwait_idle+0xd/0xf
>  [<c0103761>] cpu_idle+0xb0/0xe4
>  [<c031b509>] rest_init+0x5d/0x5f
> 
> This is not a new problem. It was pointed out some time ago already,
> but now the WARN_ON() finally made it into mainline :)
> 
> The fix is not obvious, as this code seems to be called from various
> call sites.

Hm, do you have lockdep enabled? If not, does lockdep make this go away?
Because lockdep will set IRQF_DISABLED for all interrupt handlers, and
unless that flag is set, handle_IRQ_event will reenable interrupts while
the handler is running. And ahci_interrupt only uses a plain spin_lock,
so interrupts keep being enabled. The patch below should help with that.

Hmhm, maybe that also solves the deadlock you saw? Dunno...

I can't come up with an useful commit message right now, but I'll resend
in suitable form for submission if that thing actually works.

Björn


diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 1db93b6..ae3dbc8 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -1739,6 +1739,7 @@ static irqreturn_t ahci_interrupt(int irq, void *dev_instance)
 	unsigned int i, handled = 0;
 	void __iomem *mmio;
 	u32 irq_stat, irq_ack = 0;
+	unsigned long flags;
 
 	VPRINTK("ENTER\n");
 
@@ -1751,7 +1752,7 @@ static irqreturn_t ahci_interrupt(int irq, void *dev_instance)
 	if (!irq_stat)
 		return IRQ_NONE;
 
-	spin_lock(&host->lock);
+	spin_lock_irqsave(&host->lock, flags);
 
 	for (i = 0; i < host->n_ports; i++) {
 		struct ata_port *ap;
@@ -1778,7 +1779,7 @@ static irqreturn_t ahci_interrupt(int irq, void *dev_instance)
 		handled = 1;
 	}
 
-	spin_unlock(&host->lock);
+	spin_unlock_irqrestore(&host->lock, flags);
 
 	VPRINTK("EXIT\n");
 
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