linux-ext4 - Re: ext4: Rate limit printk in buffer_io

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Date:	Thu, 11 Jul 2013 22:44:12 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Anatol Pomazau <anatol@...gle.com>
Cc:	linux-ext4@...r.kernel.org,
	Anatol Pomozov <anatol.pomozov@...il.com>
Subject: Re: ext4: Rate limit printk in buffer_io_error()

On Tue, Jul 09, 2013 at 04:01:38PM -0700, Anatol Pomazau wrote:
> From: Anatol Pomozov <anatol.pomozov@...il.com>
> 
> If there are a lot of outstanding buffered IOs when a device is
> taken offline (due to hardware errors etc), ext4_end_bio prints
> out a message for each failed logical block. While this is desirable,
> we see thousands of such lines being printed out before the
> serial console gets overwhelmed, causing ext4_end_bio() wait for
> the printk to complete.
> 
> This in itself isn't a disaster, except for the detail that this
> function is being called with the queue lock held.
> This causes any other function in the block layer
> to spin on its spin_lock_irqsave while the serial console is
> draining. If NMI watchdog is enabled on this machine then it
> eventually comes along and shoots the machine in the head.
> 
> The end result is that losing any one disk causes the machine to
> go down. This patch rate limits the printk to bandaid around the
> problem.
> 
> Tested: xfstests
> Change-Id: I8ab5690dcf4f3a67e78be147d45e489fdf4a88d8
> Signed-off-by: Anatol Pomozov <anatol.pomozov@...il.com>

Thanks, applied.

					- Ted
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