Date: Tue, 8 Nov 2011 12:47:00 -0800 From: Navdeep Parhar <nparhar@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: incorrect parent refcounting in subr_firmware.c? Message-ID: <20111108204700.GA1542@itx> In-Reply-To: <201111081000.27332.jhb@freebsd.org> References: <CAPFoGT9bLzAStkUnSfsBm0F6gmGuCM6kQRHQxa%2Bbsah4mQvQVw@mail.gmail.com> <201111081000.27332.jhb@freebsd.org>
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On Tue, Nov 08, 2011 at 10:00:27AM -0500, John Baldwin wrote: > On Wednesday, November 02, 2011 3:56:29 pm Navdeep Parhar wrote: > > I built a KLD with multiple firmware images, as shown here: > > > > KMOD=foo > > FIRMWS= foo.bin:foo:1.0.0.0 > > FIRMWS+=bar.bin:bar:1.0.0.0 > > FIRMWS+= ... > > .include <bsd.kmod.mk> > > > > "foo" is the parent firmware and a firmware_get(foo) can autoload the > > KLD. "bar" and the rest are available only if the KLD is loaded (by > > whatever means). This is reasonable and works as expected. But if I > > just get and then put "foo" back, the KLD is not unloaded automatically. > > > > The problem is that a reference is placed on the parent firmware when > > the other firmwares are registered (during module load). I think this > > reference should be placed during firmware_get on the child. > > > > What do people think about the attached patch? It fixes things for me. > > Hmm, what about the use case where a driver does: > > f = firmware_get("foo"); > firmware_put(f) > f = firmware_get("bar"); > firmware_put(f) > > Is that going to trigger multiple loads/unloads with this change? Without the patch, the get(bar) always works. But that's because the KLD is stuck in memory (it's not auto-unloaded even after the two puts and it can't be unloaded manually either). With the patch, get(bar) does not work after put(foo, FIRMWARE_UNLOAD). This is correct behaviour as documented in firmware(9) - the parent firmware is the only one that the kernel can locate with a simple name match. Once the KLD is unloaded, the kernel can't find bar. (The get would probably work after a put(foo, 0) because the KLD won't get unloaded without a FW_UNLOAD. But I'm not interested in keeping it around forever so I always specify FW_UNLOAD). As long as I put all the images back this way, the KLD is auto-unloaded at the end. Without the patch it just stays around forever. get(foo) /* autoloads foo.ko which has the "bar" image too. */ get(bar) put(bar, FIRMWARE_UNLOAD) put(foo, FIRMWARE_UNLOAD) /* KLD auto-unloaded, user happy. */ Regards, Navdeep
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