Re: [PATCH] SCSI: Fix some locking issues

[Elias Oltmanns <eo@nebensachen.de>]

James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> On Wed, 2008-07-02 at 17:59 +0200, Elias Oltmanns wrote:
>> James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
[...]
>> > unless we get down to zero depth in which case the decrements are done
>> > under lock.
>> 
>> Sorry, but this simply doesn't resolve the matter at hand.
>> scsi_finish_command() can change (host|device)_blocked values to zero at
>> any time currently *not* protected by any lock. In much the same way
>> scsi_queue_insert() can change these values from zero to something else
>> at any time.
>
> Look more closely at the requirements for the decrements:  There have to
> be no outstanding commands: nothing can be in scsi_finish_command for
> the device (or the host for host_blocked).

Yes, I agree as far as the decrements are concerned. There still is the
check

if (sdev->device_blocked)

which can happen while ->device_blocked is changed either by
scsi_finish_command() or scsi_queue_insert(). If I understand Matthew and
you correctly, this doesn't pose any problem because assigning an int is
an atomic operation anyway.

Thanks for explaining,

Elias