Re: kernel panic happens when disconnecting Bluetooth headset

[Nick Pelly <npelly@google.com>]

On Mon, Sep 21, 2009 at 5:52 PM, Nick Pelly <npelly@google.com> wrote:
> On Mon, Sep 14, 2009 at 2:10 AM, Lan Zhu <zhu.lan.cn@gmail.com> wrote:
>> Hi Marcel,
>>
>> 2009/9/12 Marcel Holtmann <marcel@holtmann.org>:
>>> Hi Zhu,
>>>
>>>> >> We met a issue that kernel panic happens when disconnecting some ki=
nds
>>>> >> of Bluetooth headset, then we did some analysis and made some chang=
es
>>>> >> on kernel code which have avoided the panic happening. Would you
>>>> >> please help to check if our analysis and fix is correct?
>>>> >>
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> Issue description
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> On Android platform(kernel 2.6.29), disconnecting Bluetooth headset
>>>> >> may cause kernel panic on certain conditions.
>>>> >>
>>>> >> (Pre-condition is android paired with headset.)
>>>> >> Initiate the connection from android, disconnect it from android, r=
esult is OK.
>>>> >> Initiate the connection from android, disconnect it from headset, r=
esult is OK.
>>>> >> Initiate the connection from headset, disconnect it from headset, r=
esult is OK.
>>>> >> Initiate the connection from headset, disconnect it from android, f=
or
>>>> >> Motorola H12 headset, result is OK.
>>>> >> Initiate the connection from headset, disconnect it from android, f=
or
>>>> >> Motorola H620/560 headset, result is kernel panic.
>>>> >>
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> Kernel panic point
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> kernel panic at __list_del() in the function rfcomm_session_del() ,
>>>> >> panic reason is "Unable to handle kernel paging request at virtual
>>>> >> address 00200200"
>>>> >>
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> Kernel log analysis
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> rfcomm_session_del() is still called after the session entry is
>>>> >> removed from the list. Then __list_del() will cause kernel panic
>>>> >> because of the incorrect pointer. This situation occurs when callin=
g
>>>> >> rfcomm_recv_ua() when the socket state is BT_CLOSED . So we need to
>>>> >> find out why the socket state become BT_CLOSED before we calling
>>>> >> rfcomm_recv_ua().
>>>> >>
>>>> >> # [ =A0171.677429] rfcomm_sock_sendmsg: sock ce9a0960, sk cc5c4c00
>>>> >> [ =A0171.683532] rfcomm_dlc_send: dlc cd3fe920 mtu 255 len 14
>>>> >> [ =A0171.689422] rfcomm_process_rx: session cc751be0 state 1 qlen 0
>>>> >> [ =A0171.695709] rfcomm_process_rx: @@@ @@@ sk_state =3D 1
>>>> >> [ =A0171.701110] rfcomm_process_dlcs: session cc751be0 state 1
>>>> >> [ =A0171.706939] rfcomm_process_tx: dlc cd3fe920 state 1 cfc 40
>>>> >> rx_credits 33 tx_credits 31
>>>> >> [ =A0171.715515] rfcomm_send_frame: session cc751be0 len 18
>>>> >> [ =A0171.721130] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 3
>>>> >> [ =A0174.127807] rfcomm_sock_sendmsg: sock ce9a0960, sk cc5c4c00
>>>> >> [ =A0174.134490] rfcomm_dlc_send: dlc cd3fe920 mtu 255 len 6
>>>> >> [ =A0174.141540] rfcomm_process_rx: session cc751be0 state 1 qlen 0
>>>> >> [ =A0174.148498] rfcomm_process_rx: @@@ @@@ sk_state =3D 1
>>>> >> [ =A0174.154968] rfcomm_process_dlcs: session cc751be0 state 1
>>>> >> [ =A0174.161437] rfcomm_process_tx: dlc cd3fe920 state 1 cfc 40
>>>> >> rx_credits 33 tx_credits 30
>>>> >> [ =A0174.171173] rfcomm_send_frame: session cc751be0 len 10
>>>> >> [ =A0174.177642] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 3
>>>> >> [ =A0174.205932] rfcomm_sock_release: sock ce9a0960, sk cc5c4c00
>>>> >> [ =A0174.212707] rfcomm_sock_shutdown: sock ce9a0960, sk cc5c4c00
>>>> >> [ =A0174.220031] __rfcomm_sock_close: sk cc5c4c00 state 1 socket ce=
9a0960
>>>> >> [ =A0174.227508] __rfcomm_dlc_close: dlc cd3fe920 state 1 dlci 20 e=
rr 0
>>>> >> session cc751be0
>>>> >> [ =A0174.236877] rfcomm_send_disc: cc751be0 dlci 20
>>>> >> [ =A0174.242706] rfcomm_send_frame: session cc751be0 len 4
>>>> >> [ =A0174.248962] rfcomm_dlc_set_timer: dlc cd3fe920 state 8 timeout=
 2560
>>>> >> [ =A0174.256835] rfcomm_sock_kill: sk cc5c4c00 state 1 refcnt 2
>>>> >> [ =A0174.263336] rfcomm_sock_destruct: sk cc5c4c00 dlc cd3fe920
>>>> >> [ =A0174.399444] rfcomm_l2data_ready: ccf70400 bytes 4
>>>> >> [ =A0174.404724] rfcomm_process_rx: session cc751be0 state 1 qlen 1
>>>> >> [ =A0174.411010] rfcomm_process_rx: @@@ @@@ sk_state =3D 1
>>>> >> [ =A0174.416412] rfcomm_recv_ua: session cc751be0 state 1 dlci 20
>>>> >> [ =A0174.422515] __rfcomm_dlc_close: dlc cd3fe920 state 9 dlci 20 e=
rr 0
>>>> >> session cc751be0
>>>> >> [ =A0174.430816] rfcomm_dlc_clear_timer: dlc cd3fe920 state 9
>>>> >> [ =A0174.436553] rfcomm_dlc_unlink: dlc cd3fe920 refcnt 1 session c=
c751be0
>>>> >> [ =A0174.443572] rfcomm_dlc_free: cd3fe920
>>>> >> [ =A0174.447570] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 3
>>>> >> [ =A0174.454528] rfcomm_send_disc: cc751be0 dlci 0
>>>> >> [ =A0174.459259] rfcomm_send_frame: session cc751be0 len 4
>>>> >> [ =A0174.464904] rfcomm_process_dlcs: session cc751be0 state 8
>>>> >> [ =A0174.470703] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 2
>>>> >> [ =A0174.898284] rfcomm_l2data_ready: ccf70400 bytes 4
>>>> >> [ =A0174.903442] rfcomm_l2state_change: ccf70400 state 9
>>>> >> [ =A0174.908874] rfcomm_process_rx: session cc751be0 state 8 qlen 1
>>>> >> [ =A0174.915130] rfcomm_process_rx: @@@ @@@ sk_state =3D 9
>>>> >> [ =A0174.920562] rfcomm_recv_ua: session cc751be0 state 8 dlci 0
>>>> >> [ =A0174.926574] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 2
>>>> >> [ =A0174.933532] rfcomm_process_rx: @@@ @@@ sk_state =3D=3D BT_CLOS=
ED , s->initiator=3D0
>>>> >> [ =A0174.941253] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 1
>>>> >> [ =A0174.948211] rfcomm_session_del: session cc751be0 state 8
>>>> >> [ =A0174.953918] @@@@ in rfcomm_session_del()
>>>> >> [ =A0174.958312] @@@@ s->list =3D cc751be0
>>>> >> [ =A0174.962097] @@@@ s->list.next =3D ccbfe9a0
>>>> >> [ =A0174.966369] @@@@ s->list.prev =3D c047d524
>>>> >> [ =A0174.970733] @@@@ list is valid, call list_del()
>>>> >> [ =A0174.975646] @@@@ after list_del()
>>>> >> [ =A0174.979278] @@@@ s->list =3D cc751be0
>>>> >> [ =A0174.983184] @@@@ s->list.next =3D 00100100
>>>> >> [ =A0174.987457] @@@@ s->list.prev =3D 00200200
>>>> >> [ =A0174.991729] rfcomm_session_close: session cc751be0 state 8 err=
 104
>>>> >> [ =A0174.998504] rfcomm_session_put: in rfcomm_session_put, s->refc=
nt =3D 1
>>>> >> [ =A0175.005310] rfcomm_session_del: session cc751be0 state 9
>>>> >> [ =A0175.011169] @@@@ in rfcomm_session_del()
>>>> >> [ =A0175.015441] @@@@ s->list =3D cc751be0
>>>> >> [ =A0175.019409] @@@@ s->list.next =3D 00100100
>>>> >> [ =A0175.023651] @@@@ s->list.prev =3D 00200200
>>>> >> [ =A0175.027923] @@@@ list is valid, call list_del()
>>>> >> [ =A0175.032958] Unable to handle kernel paging request at virtual
>>>> >> address 00200200
>>>> >> [ =A0175.040679] pgd =3D c0004000
>>>> >> [ =A0175.043792] [00200200] *pgd=3D00000000
>>>> >> [ =A0175.047821] Internal error: Oops: 817 [#1]
>>>> >> [ =A0175.052246] Modules linked in:
>>>> >> [ =A0175.055725] CPU: 0 =A0 =A0Not tainted =A0(2.6.29-omap1-dirty #=
34)
>>>> >> [ =A0175.061859] PC is at rfcomm_session_del+0x6c/0x108
>>>> >> [ =A0175.067047] LR is at release_console_sem+0x190/0x1a0
>>>> >> [ =A0175.072509] pc : [<c033ded8>] =A0 =A0lr : [<c0066308>] =A0 =A0=
psr: 60000013
>>>> >> [ =A0175.072509] sp : cc1abf38 =A0ip : cc1abe68 =A0fp : cc1abf4c
>>>> >> [ =A0175.084960] r10: cc751c04 =A0r9 : c036d2fc =A0r8 : cc751be0
>>>> >> [ =A0175.090545] r7 : 00000068 =A0r6 : cc751c04 =A0r5 : 00000009 =
=A0r4 : cc751be0
>>>> >> [ =A0175.097656] r3 : 00100100 =A0r2 : 00100100 =A0r1 : 00200200 =
=A0r0 : c0422876
>>>> >>
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> HCI log analysis
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> Compare the hcidump log of the correct case with the one of the pan=
ic
>>>> >> case, we found there is only one difference in the message sequence=
.
>>>> >> In the panic case, headset send L2CAP Disconn_Req immediately after
>>>> >> sending rfcomm UA frame to android. We think this is the reason tha=
t
>>>> >> cause the socket state become BT_CLOSED.
>>>> >>
>>>> >> Please compare these two log, pay attention to the message directio=
n
>>>> >> of the last Disconn_Req.
>>>> >>
>>>> >>
>>>> >> Log of correct case:
>>>> >> ----------------------------
>>>> >>
>>>> >>
>>>> >> 009-09-10 15:27:28.963519 < ACL data: handle 1 flags 0x02 dlen 22
>>>> >> =A0 =A0L2CAP(d): cid 0x0047 len 18 [psm 3]
>>>> >> =A0 =A0 =A0RFCOMM(d): UIH: cr 0 dlci 20 pf 0 ilen 14 fcs 0xeb
>>>> >> =A0 =A0 =A00000: 0d 0a 2b 43 49 45 56 3a =A020 37 2c 33 0d 0a =A0 =
=A0 =A0 =A0..+CIEV: 7,3..
>>>> >> 009-09-10 15:27:28.967272 > HCI Event: Number of Completed Packets =
(0x13) plen
>>>> >>
>>>> >> =A0 =A0handle 1 packets 1
>>>> >> 009-09-10 15:27:29.243945 < ACL data: handle 1 flags 0x02 dlen 8
>>>> >> =A0 =A0L2CAP(d): cid 0x0047 len 4 [psm 3]
>>>> >> =A0 =A0 =A0RFCOMM(s): DISC: cr 0 dlci 20 pf 1 ilen 0 fcs 0x7d
>>>> >> 009-09-10 15:27:29.247363 > HCI Event: Number of Completed Packets =
(0x13) plen
>>>> >>
>>>> >> =A0 =A0handle 1 packets 1
>>>> >> 009-09-10 15:27:29.274890 > 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
>>>> >> 009-09-10 15:27:29.296343 < ACL data: handle 1 flags 0x02 dlen 8
>>>> >> =A0 =A0L2CAP(d): cid 0x0047 len 4 [psm 3]
>>>> >> =A0 =A0 =A0RFCOMM(s): DISC: cr 0 dlci 0 pf 1 ilen 0 fcs 0x9c
>>>> >> 009-09-10 15:27:29.298480 > HCI Event: Number of Completed Packets =
(0x13) plen
>>>> >>
>>>> >> =A0 =A0handle 1 packets 1
>>>> >> 009-09-10 15:27:29.319873 > 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
>>>> >> 009-09-10 15:27:29.320727 < ACL data: handle 1 flags 0x02 dlen 12
>>>> >> =A0 =A0L2CAP(s): Disconn req: dcid 0x0047 scid 0x0040
>>>> >> 009-09-10 15:27:29.323474 > HCI Event: Number of Completed Packets =
(0x13) plen
>>>> >>
>>>> >> =A0 =A0handle 1 packets 1
>>>> >> 009-09-10 15:27:29.337237 > ACL data: handle 1 flags 0x02 dlen 12
>>>> >> =A0 =A0L2CAP(s): Disconn rsp: dcid 0x0047 scid 0x0040
>>>> >>
>>>> >>
>>>> >>
>>>> >>
>>>> >> log of panic case:
>>>> >> ------------------------
>>>> >>
>>>> >>
>>>> >>
>>>> >> 2009-09-10 13:34:24.020208 < ACL data: handle 1 flags 0x02 dlen 22
>>>> >> =A0 =A0 L2CAP(d): cid 0x0041 len 18 [psm 3]
>>>> >> =A0 =A0 =A0 RFCOMM(d): UIH: cr 0 dlci 20 pf 0 ilen 14 fcs 0xeb
>>>> >> =A0 =A0 =A0 0000: 0d 0a 2b 43 49 45 56 3a =A020 37 2c 33 0d 0a =A0 =
=A0 =A0 =A0..+CIEV: 7,3..
>>>> >> 2009-09-10 13:34:24.281256 > HCI Event: Number of Completed Packets=
 (0x13) plen
>>>> >> 5
>>>> >> =A0 =A0 handle 1 packets 1
>>>> >> 2009-09-10 13:34:24.083580 < ACL data: handle 1 flags 0x02 dlen 8
>>>> >> =A0 =A0 L2CAP(d): cid 0x0041 len 4 [psm 3]
>>>> >> =A0 =A0 =A0 RFCOMM(s): DISC: cr 0 dlci 20 pf 1 ilen 0 fcs 0x7d
>>>> >> 2009-09-10 13:34:24.529442 > HCI Event: Number of Completed Packets=
 (0x13) plen
>>>> >> 5
>>>> >> =A0 =A0 handle 1 packets 1
>>>> >> 2009-09-10 13:34:24.531914 > ACL data: handle 1 flags 0x02 dlen 8
>>>> >> =A0 =A0 L2CAP(d): cid 0x0040 len 4 [psm 3]
>>>> >> =A0 =A0 =A0 RFCOMM(s): UA: cr 0 dlci 20 pf 1 ilen 0 fcs 0x57
>>>> >> 2009-09-10 13:34:24.533135 < ACL data: handle 1 flags 0x02 dlen 8
>>>> >> =A0 =A0 L2CAP(d): cid 0x0041 len 4 [psm 3]
>>>> >> =A0 =A0 =A0 RFCOMM(s): DISC: cr 0 dlci 0 pf 1 ilen 0 fcs 0x9c
>>>> >> 2009-09-10 13:34:25.028649 > HCI Event: Number of Completed Packets=
 (0x13) plen
>>>> >> 5
>>>> >> =A0 =A0 handle 1 packets 1
>>>> >> 2009-09-10 13:34:25.032128 > ACL data: handle 1 flags 0x02 dlen 8
>>>> >> =A0 =A0 L2CAP(d): cid 0x0040 len 4 [psm 3]
>>>> >> =A0 =A0 =A0 RFCOMM(s): UA: cr 0 dlci 0 pf 1 ilen 0 fcs 0xb6
>>>> >> 2009-09-10 13:34:25.032341 > ACL data: handle 1 flags 0x02 dlen 12
>>>> >> =A0 =A0 L2CAP(s): Disconn req: dcid 0x0040 scid 0x0041
>>>> >> 2009-09-10 13:34:25.032646 < ACL data: handle 1 flags 0x02 dlen 12
>>>> >> =A0 =A0 L2CAP(s): Disconn rsp: dcid 0x0040 scid 0x0041
>>>> >>
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> Analysis Result
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> For some kinds of Bluetooth headset such as Motorola H560/H620 whic=
h
>>>> >> are based on BCM2044S, they will send L2CAP Disconn_Req command rig=
ht
>>>> >> after sending rfcomm UA frame. This L2CAP Disconn_Req will cause th=
e
>>>> >> rfcomm socket state become BT_CLOSED before completely handling UA
>>>> >> frame, thus it will cause kernel panic. I think we can ignore the
>>>> >> received rfcomm frames if socket state is BT_CLOSED, because it
>>>> >> doesn't make sense in the BT_CLOSED state.
>>>> >>
>>>> >>
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> Changed Code
>>>> >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>>>> >> We changed the code in the function rfcomm_process_rx() in
>>>> >> net/bluetooth/rfcomm/core.c, check the socket state first before
>>>> >> handling the received framew. If the socket state is BT_CLOSED, we
>>>> >> don't handle any rfcomm frames but just close the session.
>>>> >>
>>>> >> The change is like below
>>>> >>
>>>> >> + =A0 =A0 =A0 if (sk->sk_state !=3D BT_CLOSED) {
>>>> >> =A0 =A0 =A0 =A0 /* Get data directly from socket receive queue with=
out copying it. */
>>>> >> =A0 =A0 =A0 =A0 while ((skb =3D skb_dequeue(&sk->sk_receive_queue))=
) {
>>>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 skb_orphan(skb);
>>>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm_recv_frame(s, skb);
>>>> >> =A0 =A0 =A0 =A0 }
>>>> >> -
>>>> >> - =A0 =A0 =A0 if (sk->sk_state =3D=3D BT_CLOSED) {
>>>> >> + =A0 =A0 =A0 } else {
>>>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (!s->initiator)
>>>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm_session_put(=
s);
>>>> >>
>>>> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rfcomm_session_close(s, sk->sk_err)=
;
>>>> >> =A0 =A0 =A0 =A0 =A0}
>>>> >
>>>> > so I do see the issue here, but I don't agree with the fix since it
>>>> > changes behavior that might cause other issues. So in case the frame
>>>> > processing leads to sk->sk_state =3D=3D BT_CLOSED we are not closing=
 the
>>>> > connection anymore if we make it depend on a state before the frame
>>>> > processing. And nothing guarantees that rfcomm_process_rx gets sched=
uled
>>>> > again.
>>>> >
>>>> > diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core=
.c
>>>> > index 94b3388..606143b 100644
>>>> > --- a/net/bluetooth/rfcomm/core.c
>>>> > +++ b/net/bluetooth/rfcomm/core.c
>>>> > @@ -1798,12 +1798,16 @@ static inline void rfcomm_process_rx(struct =
rfcomm_session *s)
>>>> >
>>>> > =A0 =A0 =A0 =A0BT_DBG("session %p state %ld qlen %d", s, s->state, s=
kb_queue_len(&sk->sk_receive_queue));
>>>> >
>>>> > + =A0 =A0 =A0 rfcomm_session_hold(s);
>>>> > +
>>>> > =A0 =A0 =A0 =A0/* Get data directly from socket receive queue withou=
t copying it. */
>>>> > =A0 =A0 =A0 =A0while ((skb =3D skb_dequeue(&sk->sk_receive_queue))) =
{
>>>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0skb_orphan(skb);
>>>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0rfcomm_recv_frame(s, skb);
>>>> > =A0 =A0 =A0 =A0}
>>>> >
>>>> > + =A0 =A0 =A0 rfcomm_session_put(s);
>>>> > +
>>>> > =A0 =A0 =A0 =A0if (sk->sk_state =3D=3D BT_CLOSED) {
>>>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (!s->initiator)
>>>> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0rfcomm_session_put(s)=
;
>>>> >
>>>> > What does the above patch do for you? Since if I read it correctly, =
then
>>>> > the rfcomm_recv_ua causes the rfcomm_session_put to trigger the clos=
ing
>>>> > of the session. And then in this case it is delayed until after all
>>>> > frames are processed.
>>>> >
>>>> >
>>>>
>>>> I've tried your patch but unfortunately kernel panic still happened.
>>>>
>>>> From the log I noticed that if rfcomm_l2state_change is called before
>>>> rfcomm_process_rx, kernel panic will happen definitely.
>>>>
>>>> Below lines are in the correct log,
>>>>
>>>> [ =A0139.323852] rfcomm_l2data_ready: ccf70000 bytes 4
>>>> [ =A0139.346252] rfcomm_process_rx: session ccb94ce0 state 8 qlen 1
>>>> ...
>>>> [ =A0139.457519] rfcomm_l2state_change: ccf70000 state 9
>>>> (disconnect ok)
>>>>
>>>> In the above case, when process_rx, the code in the condition "if
>>>> (sk->sk_state =3D=3D BT_CLOSED)" will never run.
>>>>
>>>> Below lines are in the panic log,
>>>>
>>>> [ =A0174.898284] rfcomm_l2data_ready: ccf70400 bytes 4
>>>> [ =A0174.903442] rfcomm_l2state_change: ccf70400 state 9
>>>> [ =A0174.908874] rfcomm_process_rx: session cc751be0 state 8 qlen 1
>>>> ...
>>>> ( then panic)
>>>>
>>>> In the above case, sk_state is changed to 9 (BT_CLOSED) firstly, =A0th=
en
>>>> process_rx, so the code in the condition "if (sk->sk_state =3D=3D
>>>> BT_CLOSED) " will be run, it will call session_put twice. I think this
>>>> is the root cause of panic.
>>>
>>> I know why it happens, that is not the problem. My point is not to brea=
k
>>> current scheduling assumptions.
>>>
>>> So if you move the rfcomm_session_put() now at the end of the function,
>>> then it should be fine, right?
>>>
>>> Regards
>>>
>>> Marcel
>>>
>>>
>>>
>>
>> You are right. I moved the rfcomm_session_put() at the end of
>> rfcomm_process_tx() then kernel panic doesn't happen any longer.
>>
>> The changed code is like below,
>>
>> @@ -1796,6 +1796,8 @@ static inline void rfcomm_process_rx(struct rfcomm=
_session
>>
>> =A0 =A0 =A0 =A0BT_DBG("session %p state %ld qlen %d", s, s->state, skb_q=
ueue_len(&sk->s
>>
>> + =A0 =A0 =A0 rfcomm_session_hold(s);
>> +
>> =A0 =A0 =A0 =A0/* Get data directly from socket receive queue without co=
pying it. */
>> =A0 =A0 =A0 =A0while ((skb =3D skb_dequeue(&sk->sk_receive_queue))) {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0skb_orphan(skb);
>> @@ -1808,6 +1810,8 @@ static inline void rfcomm_process_rx(struct rfcomm=
_session
>>
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0rfcomm_session_close(s, sk->sk_err);
>> =A0 =A0 =A0 =A0}
>> +
>> + =A0 =A0 =A0 rfcomm_session_put(s);
>> =A0}
>>
>> =A0static inline void rfcomm_accept_connection(struct rfcomm_session *s)
>>
>> Please submit this change to bluez release.
>
>
> Unfortunately, with this change I get a panic disconnecting from
> Motorola H270 in the case that the headset initiated RFCOMM and we
> disconnect RFCOMM.
>
> Here is the hcidump:
>
> 2009-09-21 17:22:37.384811 < ACL data: handle 1 flags 0x02 dlen 22
> =A0 =A0L2CAP(d): cid 0x0041 len 18 [psm 3]
> =A0 =A0 =A0RFCOMM(d): UIH: cr 0 dlci 20 pf 0 ilen 14 fcs 0xeb
> =A0 =A0 =A00000: 0d 0a 2b 43 49 45 56 3a =A020 37 2c 33 0d 0a =A0 =A0 =A0=
 =A0..+CIEV: 7,3..
> 2009-09-21 17:22:37.502273 > HCI Event: Number of Completed Packets
> (0x13) plen 5
> =A0 =A0handle 1 packets 1
> 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
> 2009-09-21 17:22:39.029526 < ACL data: handle 1 flags 0x02 dlen 12
> =A0 =A0L2CAP(s): Disconn rsp: dcid 0x0040 scid 0x0041
> 2009-09-21 17:22:39.136581 > HCI Event: Number of Completed Packets
> (0x13) plen 5
> =A0 =A0handle 1 packets 1
> 2009-09-21 17:22:41.337203 > HCI Event: Disconn Complete (0x05) plen 4
> =A0 =A0status 0x00 handle 1 reason 0x13
> =A0 =A0Reason: Remote User Terminated Connection
>
> And the panic:
>
> <7>[ 3161.665557] rfcomm:rfcomm_session_del: session c9c06ad0 state 9
> <7>[ 3161.671905] l2cap:l2cap_sock_release: sock cea04360, sk c97f02f8
> <7>[ 3161.678497] l2cap:l2cap_sock_shutdown: sock cea04360, sk c97f02f8
> <7>[ 3161.685028] l2cap:l2cap_sock_kill: sk c97f02f8 state 9
> <7>[ 3161.695587] l2cap:l2cap_sock_destruct: sk c97f02f8
> <4>[ 3161.700805] npelly 1911 rfcomm_process_sessions session c9c06ad0
> refcnt 1802201963
> <7>[ 3161.709014] rfcomm:rfcomm_process_dlcs: session c9c06ad0 state 1802=
201963
> <7>[ 3161.716308] rfcomm:rfcomm_process_dlcs: session c9c06ad0 dlc 6b6b6b=
6b
> <1>[ 3161.726776] Unable to handle kernel paging request at virtual
> address 6b6b6b6b
> <1>[ 3161.734619] pgd =3D c0004000
> <1>[ 3161.737609] [6b6b6b6b] *pgd=3D00000000
> <4>[ 3161.741638] Internal error: Oops: 5 [#1] PREEMPT
> <4>[ 3161.746734] Modules linked in:
> <4>[ 3161.750213] CPU: 0 =A0 =A0Not tainted
> (2.6.29-omap1-07358-g9a3fd55-dirty #206)
> <4>[ 3161.757629] PC is at rfcomm_process_dlcs+0x108/0x590
> <4>[ 3161.762969] LR is at preempt_schedule+0x44/0x54
> <4>[ 3161.767852] pc : [<c03911f4>] =A0 =A0lr : [<c03a27c4>] =A0 =A0psr: =
60000113
> <4>[ 3161.767883] sp : ccdf9e80 =A0ip : ccdf9dd8 =A0fp : ccdf9edc
> <4>[ 3161.780273] r10: 00000000 =A0r9 : c9c06af4 =A0r8 : c9c06ad0
> <4>[ 3161.786010] r7 : 00000000 =A0r6 : c9c06ad0 =A0r5 : c4c68680 =A0r4 :=
 6b6b6b6b
> <4>[ 3161.792968] r3 : c9c06ae0 =A0r2 : ccdf8000 =A0r1 : c61a8940 =A0r0 :=
 0000004c
> <4>[ 3161.800079] Flags: nZCv =A0IRQs on =A0FIQs on =A0Mode SVC_32 =A0ISA=
 ARM
> Segment kernel
> <4>[ 3161.807983] Control: 10c5387d =A0Table: 86db8019 =A0DAC: 00000017
> <4>[ 3161.814147]
> <4>[ 3161.814147] PC: 0xc0391174:
> [...]
> <4>[ 3162.973175] Backtrace:
> <4>[ 3162.976013] [<c03910ec>] (rfcomm_process_dlcs+0x0/0x590) from
> [<c03930b0>] (rfcomm_process_sessions+0x1a34/0x1a9c)
> <4>[ 3162.987579] [<c039167c>] (rfcomm_process_sessions+0x0/0x1a9c)
> from [<c03932ec>] (rfcomm_run+0x1d4/0x2ac)
> <4>[ 3162.998199] [<c0393118>] (rfcomm_run+0x0/0x2ac) from
> [<c008e7d8>] (kthread+0x5c/0x94)
> <4>[ 3163.013763] [<c008e77c>] (kthread+0x0/0x94) from [<c007c998>]
> (do_exit+0x0/0x714)
>
>
> Seems like this fix avoids the panic due to calling
> rfcomm_session_close() on a deleted session, but does not always
> address the unbalanced rfcomm_session_put() which may be the root
> cause.
>
> Lan Zhu suspected this in the original post, and his original fix does
> in fact fix this panic as well as the originally reported panic,
> because it avoids the unbalanced rfcomm_session_put().
>
> Marcel I know you are concerned about the original fix changing
> scheduling assumptions, are you able to comment on this further?
>
> Are there any other suggestions for patches for this issue? I have
> spent the best part of the day trying to figure this one out, but the
> recounting in the rfcomm core is quite subtle and I think it really
> needs someone familiar with the code to have a quick look and come up
> with the safest patch. I can run tests.
>
> In the mean time, I am doing some testing of Lan Zhu's original fix
> and if there are no better suggestions we will run with that one for
> Android.
>
> Nick
>
>
> Some more analysis:
>
> With the RFCOMM connection in idle there are 2 references on s->refcnt
>
> However three references are removed during disconnect with the H270
> - rfcomm_process_sessions() -> __rfcomm_dlc_close() -> rfcomm_dlc_unlink(=
)
> - rfcomm_process_sessions() -> rfcomm_process_rx() -> rfcomm_recv_ua()
> with dlci =3D 0 and s->state =3D BT_DISCONN
> - rfcomm_process_sessions() -> rfcomm_process_rx() with sk_state =3D
> BT_CLOSED and s->initiator =3D 0
>
> in that order.
>
> On another headset, for example the Moto H350, we only see the first
> two references removed during disconnect.
>
> - rfcomm_process_sessions() -> __rfcomm_dlc_close() -> rfcomm_dlc_unlink(=
)
> - rfcomm_process_sessions() -> rfcomm_process_rx() -> rfcomm_recv_ua()
> with dlci =3D 0 and s->state =3D BT_DISCONN
>

How about this. We still call rfcomm_process_rx(), but avoid the
rfcomm_session_put() due to RFCOMM UA when the socket state is
BT_CLOSED.

It is less invasive, so might address Marcel's concerns with regard to
scheduling changes.


diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index c109a3a..333c6e9 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1105,6 +1105,8 @@ static int rfcomm_recv_ua(struct rfcomm_session
*s, u8 dlci)
                }
        } else {
                /* Control channel */
+               struct socket *sock =3D s->sock;
+               struct sock *sk =3D sock->sk;
                switch (s->state) {
                case BT_CONNECT:
                        s->state =3D BT_CONNECTED;
@@ -1112,7 +1114,8 @@ static int rfcomm_recv_ua(struct rfcomm_session
*s, u8 dlci)
                        break;

                case BT_DISCONN:
-                       rfcomm_session_put(s);
+                       if (sk->sk_state !=3D BT_CLOSED)
+                               rfcomm_session_put(s);
                        break;
                }
        }