Date: Thu, 23 Sep 2010 10:42:33 -0700 From: "Ricky Charlet" <RCharlet@adaranet.com> To: John Baldwin <jhb@freebsd.org>, "freebsd-drivers@freebsd.org" <freebsd-drivers@freebsd.org> Subject: RE: newbie trouble with destroy_dev Message-ID: <32AB5C9615CC494997D9ABB1DB12783C024C950492@SJ-EXCH-1.adaranet.com> In-Reply-To: <201009230949.12884.jhb@freebsd.org> References: <32AB5C9615CC494997D9ABB1DB12783C024C95033B@SJ-EXCH-1.adaranet.com> <201009230949.12884.jhb@freebsd.org>
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Thanks.
That totally worked. Lesson learned =3D destroy_dev sooner than des=
troy cv's and mutexes's and internal state.
One question though... I did not find any "DYING" flag in relation =
to cv's or mutexes. So I just skipped that step in your advice. I only foun=
d the string "DYING" in relation to jails, sound-drivers, some network stuf=
f and ipsec. Will you give me a little more specific pointer to what "DYING=
" flag you were referring to?
FYI, my userland program sitting in the read loop exited cleanly an=
d got errno=3DENXIO, which is beautiful.
Thanks again.
---
Ricky Charlet
Adara Networks
USA 408-433-4942
-----Original Message-----
From: John Baldwin [mailto:jhb@freebsd.org]
Sent: Thursday, September 23, 2010 6:49 AM
To: freebsd-drivers@freebsd.org
Cc: Ricky Charlet
Subject: Re: newbie trouble with destroy_dev
On Wednesday, September 22, 2010 3:11:10 pm Ricky Charlet wrote:
> Howdy,
>
> My goal is to destroy a character device which is current=
ly
open for read. Is that allowable? I'm hoping the userland program doing the
reading will simply get a read error back (possibly with no data or truncat=
ed
data).
>
> My experience so far is that I crash the box.
>
> I'm using BSD 8.0. My program with the driver is a kerne=
l
module. Upon using the `kldunload` utility, the d_close() method is called.=
I
have tried these logic flows:
>
> Test 1
> ---------------------
> Unhook my packet-filter-hooks
> cv_broadcast;
> cv_destory
> mMtx_destroy
> destroy_dev
> free associated buffers
>
> Test 2
> --------------------
> Unhook my packet-filter-hooks
> cv_broadcast;
> cv_destory
> mMtx_destroy
> destroy_dev_sched_cb
> free associated buffers
>
> Test 3
> ----------------------
> Unhook my packet-filter-hooks
> cv_broadcast;
> cv_destory
> mMtx_destroy
> free associated buffers
>
>
> In all cases I get a kernel crash and the system reboots.
Note that the userland program has the associated charater device open and =
is
in a for-ever loop reading the fd.
>
> I'm a newbie and have not yet attached a debugger. I'll g=
o
start reading about that and trying it out while I hopefully await replies.
Call destroy_dev() earlier, before you destroy any state. Your cdevsw
routines can be invoked right up until destroy_dev() returns, so if you
destroy the mutex before destroy_dev() you might destroy it before a cdevsw
routine tries to use it. I suspect you might need something like:
unhook_packet_filters
set DYING flag (for listeners to the cv to know to exit, etc.)
cv_broadcast()
destroy_dev()
free buffers
cv_destroy()
mtx_destroy()
--
John Baldwin
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