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Date: Mon, 19 Sep 2005 06:30:23 GMT
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To: freebsd-bugs@FreeBSD.org
From: Ruslan Ermilov <ru@freebsd.org>
Cc: 
Subject: Re: kern/86306: [patch] if_em.c locks up while trying to send a
	highly fragmented packet
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The following reply was made to PR kern/86306; it has been noted by GNATS.

From: Ruslan Ermilov <ru@freebsd.org>
To: Dmitrij Tejblum <tejblum@yandex-team.ru>
Cc: FreeBSD-gnats-submit@freebsd.org
Subject: Re: kern/86306: [patch] if_em.c locks up while trying to send a highly fragmented packet
Date: Mon, 19 Sep 2005 09:29:26 +0300

 Hi Dmitrij,
 
 On Sun, Sep 18, 2005 at 11:25:35PM +0400, Dmitrij Tejblum wrote:
 > When em_encap() tries to send a very long mbuf chain (i.e. more than
 > EM_MAX_SCATTER == 64 mbufs), bus_dmamap_load_mbuf_sg() may fail with EFBIG. 
 > Then em_encap() fail, the packet is not sent and left in the output queue, 
 > and thus no futher transmission is possible.
 > 
 > Some other driver handle similar condition with m_defrag(9) function
 > (which is intended for this purpose).
 > 
 Can you please modify your patch as follows:
 
 1) Count how much fragments are in the packet in em_encap() first, and
    do m_defrag() if it exceeeds EM_MAX_SCATTER, like in if_dc.c.  If it
    is still EFBIG after that and bus_dmamap_load_mbuf_sg(), then free it
    as you do to prevent re-enqueue.
 
 2) Put BPF processing back to em_start_locked().
 
 3) Pull up to the HEAD version of the driver.
 
 
 Cheers,
 -- 
 Ruslan Ermilov
 ru@FreeBSD.org
 FreeBSD committer