linux-kernel - Re: [PATCH] cciss: Optimize scan

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Date:	Thu, 23 Apr 2015 11:11:02 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Davidlohr Bueso <dave@...olabs.net>
CC:	Mike Miller <mike.miller@...com>, Don Brace <don.brace@...s.com>,
	iss_storagedev@...com, storagedev@...s.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cciss: Optimize scan_thread

On 04/23/2015 11:06 AM, Davidlohr Bueso wrote:
> On Thu, 2015-04-23 at 10:51 -0600, Jens Axboe wrote:
>> Not that it's wrong, but this is mostly some unneeded optimizations.
>> It's not like this is in a hot path.
>
> Most definitely small optimizations, I just happened to run into
> auditing schedule calls. Still no harm in applying.

Are you sure? What happens if scan_thread() races with pci removal? The 
list was non-empty, enter the loop. PCI removal removes the device from 
the scan list. Now we grab the lock in scan_thread(), and 
unconditionally attempt to remove an entry from scan_q. Maybe something 
protects us from this, maybe it doesn't.

So IOW, I don't like your lock optimization, it's a bad idea. The 
__set_current_state() change is definitely fine, though.

-- 
Jens Axboe

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