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Date: Wed, 21 Sep 2005 23:02:50 +0400
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: John Baldwin <jhb@FreeBSD.org>
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Cc: Robert Watson <rwatson@FreeBSD.org>, Ruslan Ermilov <ru@FreeBSD.org>,
	"M. Warner Losh" <imp@bsdimp.com>, cvs-src@FreeBSD.org
Subject: cleanup of interface shutdown/detach Was: cvs commit: src/sys/dev/an
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On Wed, Sep 21, 2005 at 02:55:57PM -0400, John Baldwin wrote:
J> > 4.  Remove IFF_DRV_RUNNING check from ether_output().

<skip>

J> I think you can leave #4 in if the race doesn't hurt anything.

This check confuses people, is incorrect and useless. It confuses
people, because they think that the !IFF_DRV_RUNNING condition is
checked.  It is incorrect because upper layer must not touch/look
at if_drv_flags. It is useless because the flag is checked without
driver mutex being acquired, and thus does not protect from anything.

Yesterday I have fixed panic in em(4) that was "protected" by this
check. The correct way is to check the flag in interface start
method, with driver mutex held.

-- 
Totus tuus, Glebius.
GLEBIUS-RIPN GLEB-RIPE