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Date: Sat, 1 Oct 2005 23:15:32 +1000 (EST)
From: Bruce Evans <bde@zeta.org.au>
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To: Gleb Smirnoff <glebius@FreeBSD.org>
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Cc: net@FreeBSD.org
Subject: Re: [REVIEW/TEST] polling(4) changes
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On Fri, 30 Sep 2005, Gleb Smirnoff wrote:

> The attached patch removes:
> ...
>  - poll in trap feature. Sorry, we can't acquire mutexes in trap(). Anyone
>    used it, anyway?

This is the most broken part of DEVICE_POLLING (which I consider to be
mostly broken).  Hopefully no one used it.  Poll in trap even polled in
debugger traps, so userland could invoke polling by debugging any program,
and ether_poll() was reentered if it was debugged (in RELENG_4, there is
no relevant locking so ether_poll() then just raced itself; in old versions
of -current I think Giant locking allowed the same since Giant is recursive;
in -current I think this causes deadlock since poll_mtx is not recursive).

> The attached patch touches only em(4) and fxp(4). I will write patches for all
> other drivers ASAP. But I don't have all the hardware, so if you are using polling(4)
> and you run FreeBSD 6 or 7, please help me with testing. ATM only em(4) driver patch
> is tested.

While you are there, please fix the configuration so that DEVICE_POLLING
is a normal option.  It is very far from being a global option.

Bruce