linux-kernel - Re: sata_mv port lockup on hotplug (kernel 2.6.38.2)

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Message-ID: <4DA5BCF3.5080205@teksavvy.com>
Date:	Wed, 13 Apr 2011 11:10:43 -0400
From:	Mark Lord <kernel@...savvy.com>
To:	Bruce Stenning <b.stenning@...igovision.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>
Subject: Re: sata_mv port lockup on hotplug (kernel 2.6.38.2)

On 11-04-12 06:30 AM, Bruce Stenning wrote:
..
> I am currently inserting tracing into 2.6.38.2 to try to work out what is going
> on.  From mv_write_main_irq_mask I can see that the IRQ for each port is still
> enabled, even when ports stop responding.
..
> One thing I noticed was that there is no spinlock around the
> mv_save_cached_regs/mv_edma_cfg in mv_hardreset (unlike mv_port_start and
> mv_port_stop); why is this?

Yeah, I'm suspecting there's a loophole in the logic there somewhere.

I dusted off the 6041 reference card I have here, and played with the cables
for a while.  Managed to get one port to stop responding to hot plug fairly
quickly, though I'm not sure how/why.

Then I added a debug printk() to mv_write_main_irq_mask(),
with no other changes, and that appears to have been enough
to change the race timing so that I could no longer produce
the problem.

Bruce, here's a slightly-ugly patch that should remove all
doubt about races in the irq_mask.  Please apply it, test with it,
and let me know here if the issue goes away.

Thanks

--- old/drivers/ata/sata_mv.c	2011-04-13 11:03:07.442481426 -0400
+++ linux/drivers/ata/sata_mv.c	2011-04-13 11:07:55.224249621 -0400
@@ -1027,15 +1027,19 @@
 static void mv_set_main_irq_mask(struct ata_host *host,
 				 u32 disable_bits, u32 enable_bits)
 {
+	static spinlock_t irq_mask_lock = __SPIN_LOCK_UNLOCKED(irq_mask_lock); //
FIXME: per-host would be nicer
 	struct mv_host_priv *hpriv = host->private_data;
 	u32 old_mask, new_mask;
+	unsigned long flags;

+	spin_lock_irqsave(&irq_mask_lock, flags);
 	old_mask = hpriv->main_irq_mask;
 	new_mask = (old_mask & ~disable_bits) | enable_bits;
 	if (new_mask != old_mask) {
 		hpriv->main_irq_mask = new_mask;
 		mv_write_main_irq_mask(new_mask, hpriv);
 	}
+	spin_unlock_irqrestore(&irq_mask_lock, flags);
 }

 static void mv_enable_port_irqs(struct ata_port *ap,

View attachment "sata_mv_irq_mask_lock.patch" of type "text/x-patch" (825 bytes)