Return-Path: MIME-Version: 1.0 In-Reply-To: <508e92ca0912220820j30e08e0ar84bcf0efb0bf4f9a@mail.gmail.com> References: <113d36d80909110053ybd2c203xeda76bd36248bb17@mail.gmail.com> <113d36d80909140210n476f5826x1ae2ea621b57782c@mail.gmail.com> <35c90d960909211752u389e5d6dqbd4afe0e055c43d0@mail.gmail.com> <35c90d960909211829u71880f94j861055c61efc8c@mail.gmail.com> <35c90d960909221318m4b918d2dg3e2688a89427319a@mail.gmail.com> <508e92ca0912180620l3550bdb7w1211094681cbc87b@mail.gmail.com> <1261173555.4041.91.camel@localhost.localdomain> <35c90d960912181430t4bf36fb9gbc6ae71eeaf16602@mail.gmail.com> <1261177347.4041.103.camel@localhost.localdomain> <508e92ca0912220820j30e08e0ar84bcf0efb0bf4f9a@mail.gmail.com> From: Nick Pelly Date: Tue, 2 Feb 2010 18:11:21 -0800 Message-ID: <35c90d961002021811y737e1005va83dca54e030f976@mail.gmail.com> Subject: Re: kernel panic happens when disconnecting Bluetooth headset To: Andrei Emeltchenko Cc: Marcel Holtmann , Lan Zhu , linux-bluetooth@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 List-ID: On Tue, Dec 22, 2009 at 8:20 AM, Andrei Emeltchenko wrote: > Hi Marcel, > > On Sat, Dec 19, 2009 at 1:02 AM, Marcel Holtmann wr= ote: >> Hi Nick, >> >>> >> Processing a RFCOMM UA frame when the socket is closed and we were n= ot >>> >> the >>> >> RFCOMM initiator would cause rfcomm_session_put() to be called twice >>> >> during >>> >> rfcomm_process_rx(). This would cause a kernel panic in >>> >> rfcomm_session_close. >>> >> >>> >> This could be easily reproduced during disconnect with devices such = as >>> >> Motorola H270 that send RFCOMM UA followed quickly by L2CAP disconne= ct >>> >> request. >>> >> This hcidump for this looks like: >>> >> >>> >> 2009-09-21 17:22:37.788895 < ACL data: handle 1 flags 0x02 dlen 8 >>> >> =A0 =A0L2CAP(d): cid 0x0041 len 4 [psm 3] >>> >> =A0 =A0 =A0RFCOMM(s): DISC: cr 0 dlci 20 pf 1 ilen 0 fcs 0x7d >>> >> 2009-09-21 17:22:37.906204 > HCI Event: Number of Completed Packets >>> >> (0x13) >>> >> plen 5 >>> >> =A0 =A0handle 1 packets 1 >>> >> 2009-09-21 17:22:37.933090 > ACL data: handle 1 flags 0x02 dlen 8 >>> >> =A0 =A0L2CAP(d): cid 0x0040 len 4 [psm 3] >>> >> =A0 =A0 =A0RFCOMM(s): UA: cr 0 dlci 20 pf 1 ilen 0 fcs 0x57 >>> >> 2009-09-21 17:22:38.636764 < ACL data: handle 1 flags 0x02 dlen 8 >>> >> =A0 =A0L2CAP(d): cid 0x0041 len 4 [psm 3] >>> >> =A0 =A0 =A0RFCOMM(s): DISC: cr 0 dlci 0 pf 1 ilen 0 fcs 0x9c >>> >> 2009-09-21 17:22:38.744125 > HCI Event: Number of Completed Packets >>> >> (0x13) >>> >> plen 5 >>> >> =A0 =A0handle 1 packets 1 >>> >> 2009-09-21 17:22:38.763687 > ACL data: handle 1 flags 0x02 dlen 8 >>> >> =A0 =A0L2CAP(d): cid 0x0040 len 4 [psm 3] >>> >> =A0 =A0 =A0RFCOMM(s): UA: cr 0 dlci 0 pf 1 ilen 0 fcs 0xb6 >>> >> 2009-09-21 17:22:38.783554 > ACL data: handle 1 flags 0x02 dlen 12 >>> >> =A0 =A0L2CAP(s): Disconn req: dcid 0x0040 scid 0x0041 >>> >> >>> >> Avoid calling rfcomm_session_put() twice by skipping this call >>> >> in rfcomm_recv_ua() if the socket is closed. >>> >> >>> >> Picked from: >>> >> http://android.git.kernel.org/?p=3Dkernel/common.git;a=3Dcommit;h=3D= 1048e007842da2d6440679e1ca80f45438a6369d >>> >> >>> >> Signed-off-by: Nick Pelly >>> >> Signed-off-by: Andrei Emeltchenko >>> >> --- >>> >> =A0net/bluetooth/rfcomm/core.c | =A0 =A03 ++- >>> >> =A01 files changed, 2 insertions(+), 1 deletions(-) >>> >> >>> >> diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core= .c >>> >> index 0313e88..56ffcb8 100644 >>> >> --- a/net/bluetooth/rfcomm/core.c >>> >> +++ b/net/bluetooth/rfcomm/core.c >>> >> @@ -1148,7 +1148,8 @@ static int rfcomm_recv_ua(struct rfcomm_sessio= n >>> >> *s, u8 dlci) >>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 break; >>> >> >>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 case BT_DISCONN: >>> >> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm_session_put(s); >>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (s->sock->sk->sk_st= ate !=3D BT_CLOSED) >>> >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm= _session_put(s); >>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 break; >>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 } >>> >> =A0 =A0 =A0 =A0 } >>> > >>> > I am not a big fan of conditionally decreasing reference counts. I do >>> > think it would be better to fix this by holding an extra pair of >>> > reference counts or actually fixing the imbalance. What about the oth= er >>> > patches I proposed? >>> >>> Your proposed patch was to add an extra hold() / put() reference count >>> around the offending put(). I did test this patch, and found it does >>> not fix the underlying imbalance, it just moves the kernel panic >>> somewhere else. >>> >>> As best I can tell, my patch does address the underlying imbalance. It >>> is in production on Android phones and seems to work well. As best I >>> can tell, there is not a cleaner solution that does not involve >>> significant refactoring of rfcomm refcounting. > > We have this patch also in Nokia N900 phone. And this was the best soluti= on > for the problem mentioned. > >> the RFCOMM reference counting is something nasty and it does need to be >> re-written. One thing that needs to happen that we stop using the L2CAP >> sockets directly. We have to put a proper L2CAP in-kernel specific API >> in between that ensures we are not mixing things. That is the one issues >> that we always had in this area. >> >> Before applying this patch, I like to have additionally a comment in >> front of this conditional put call that explains a little bit the >> problem area here. The long explanation with logs etc. should be in the >> commit message. I have to make sure that we fully understand what is >> going on here and why we did it. > > What do you think about following comment: > > --- a/net/bluetooth/rfcomm/core.c > +++ b/net/bluetooth/rfcomm/core.c > @@ -1151,7 +1151,11 @@ static int rfcomm_recv_ua(struct rfcomm_session > *s, u8 dlci) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0break; > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0case BT_DISCONN: > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm_session_put(s); > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* When socket is closed an= d we are not RFCOMM > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* initiator rfcomm_proce= ss_rx already calls > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* rfcomm_session_put */ > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (s->sock->sk->sk_state != =3D BT_CLOSED) > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm_sess= ion_put(s); > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0break; > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} > =A0 =A0 =A0 =A0} > -- > Ping. Nick