Re: RFC/T: Trial fix for the bcm43xx - wpa_supplicant - NetworkManagerdeadlock

[Ray Lee]

Larry Finger wrote:
> Dan Williams wrote the following regarding this deadlock problem:
> "NM should be using wpa_supplicant underneath.  But depending on the NM
> version, NM may be issuing any one of SIWENCODE (only to clear keys),
> [S|G]IWSCAN, GIWRANGE, GIWAP, [S|G]IWMODE, [S|G]IWFREQ.  Mainly, NM
> cleans up after wpa_supplicant, gets information about the current
> connection, and does scans.  All other connection setup and handling is
> done by wpa_supplicant.  But note that NM will do any of the above
> operations at any time, no matter what wpa_supplicant is doing at that
> time.  So the locking in the driver needs to be right, but it should be
> right anyway regardless of whether either one or both of NM and
> wpa_supplicant is in the picture..."

The trace I posted in my first message (by reference,
http://madrabbit.org/~ray/messages.gz , as it's too big for the list) shows
NetworkManager and wpa_supplicant (and events/0) implicated both times. First
time:

 NetworkManage D ffff810037943258     0  4833      1          4853  4809 (NOTLB)
  ffff81002bfefbe8 0000000000000046 ffff81002bfefb98 ffff810037943080
  ffff81002e6d2100 00000000000122a6 ffffffff8062ce80 0000000000000046
  0000000000000246 ffff810037943080 ffff81002e47b3f0 ffff81002e47b3a0
 Call Trace:
  [__mutex_lock_slowpath+344/624] __mutex_lock_slowpath+0x158/0x270
  [mutex_lock+9/16] mutex_lock+0x9/0x10
  [_end+126343345/2126632680] :bcm43xx:bcm43xx_wx_get_mode+0x29/0x60
  [ioctl_standard_call+139/944] ioctl_standard_call+0x8b/0x3b0
  [wireless_process_ioctl+260/976] wireless_process_ioctl+0x104/0x3d0
  [dev_ioctl+854/944] dev_ioctl+0x356/0x3b0
  [sock_ioctl+576/624] sock_ioctl+0x240/0x270
  [do_ioctl+49/160] do_ioctl+0x31/0xa0
  [vfs_ioctl+683/720] vfs_ioctl+0x2ab/0x2d0
  [sys_ioctl+106/160] sys_ioctl+0x6a/0xa0
  [system_call+126/131] system_call+0x7e/0x83
 DWARF2 unwinder stuck at system_call+0x7e/0x83

...also in D state:

 events/0      D ffff810037fbf2d8     0     4      1             5     3 (L-TLB)
  ffff810037f05ca0 0000000000000046 0000000000000000 ffff810037fbf100
  ffff810037943080 00000000007ad810 ffff81002e47b328 ffff810035964ae0
  ffff810035964ad8 ffff81002e47ae68 ffff810035964ae0 ffff810035964ae0
 Call Trace:
  [wait_for_completion+160/240] wait_for_completion+0xa0/0xf0
  [_end+125757445/2126632680]
:ieee80211softmac:ieee80211softmac_wait_for_scan_implementation+0x7d/0x90
  [_end+125757101/2126632680]
:ieee80211softmac:ieee80211softmac_wait_for_scan+0x45/0x50
  [_end+125755609/2126632680]
:ieee80211softmac:ieee80211softmac_clear_pending_work+0x21/0x210
  [_end+125756872/2126632680] :ieee80211softmac:ieee80211softmac_stop+0x10/0x20
  [_end+126288441/2126632680] :bcm43xx:bcm43xx_select_wireless_core+0xa1/0x470
  [_end+126289490/2126632680] :bcm43xx:bcm43xx_chip_reset+0x4a/0x90
  [run_workqueue+205/288] run_workqueue+0xcd/0x120
  [worker_thread+283/352] worker_thread+0x11b/0x160
  [kthread+211/272] kthread+0xd3/0x110
  [child_rip+10/18] child_rip+0xa/0x12
 DWARF2 unwinder stuck at child_rip+0xa/0x12

 x-session-man D ffff81002ef02298     0  5625   4565  5672          4586 (NOTLB)
  ffff810028a1fad8 0000000000000046 ffffffff8062c500 ffff81002ef020c0
  ffff8100249a6040 0000000000008c5d 0000000000000000 0000000000000046
  0000000000000246 ffff81002ef020c0 ffffffff805505b0 ffffffff80550560
 Call Trace:
  [__mutex_lock_slowpath+344/624] __mutex_lock_slowpath+0x158/0x270
  [mutex_lock+9/16] mutex_lock+0x9/0x10
  [rtnetlink_rcv+44/96] rtnetlink_rcv+0x2c/0x60
  [netlink_data_ready+26/96] netlink_data_ready+0x1a/0x60
  [netlink_sendskb+51/96] netlink_sendskb+0x33/0x60
  [netlink_unicast+536/592] netlink_unicast+0x218/0x250
  [netlink_sendmsg+704/736] netlink_sendmsg+0x2c0/0x2e0
  [sock_sendmsg+271/320] sock_sendmsg+0x10f/0x140
  [sys_sendto+273/320] sys_sendto+0x111/0x140
  [system_call+126/131] system_call+0x7e/0x83
 DWARF2 unwinder stuck at system_call+0x7e/0x83


 wpa_supplican D ffff810026e9a218     0  8058      1         19402  6666 (NOTLB)
  ffff81001bf81ad8 0000000000000046 0000000000000002 ffff810026e9a040
  ffff8100072e4140 000000000001b54f 0000000000000000 0000000000000046
  0000000000000246 ffff810026e9a040 ffffffff805505b0 ffffffff80550560
 Call Trace:
  [__mutex_lock_slowpath+344/624] __mutex_lock_slowpath+0x158/0x270
  [mutex_lock+9/16] mutex_lock+0x9/0x10
  [rtnetlink_rcv+44/96] rtnetlink_rcv+0x2c/0x60
  [netlink_data_ready+26/96] netlink_data_ready+0x1a/0x60
  [netlink_sendskb+51/96] netlink_sendskb+0x33/0x60
  [netlink_unicast+536/592] netlink_unicast+0x218/0x250
  [netlink_sendmsg+704/736] netlink_sendmsg+0x2c0/0x2e0
  [sock_sendmsg+271/320] sock_sendmsg+0x10f/0x140
  [sys_sendto+273/320] sys_sendto+0x111/0x140
  [system_call+126/131] system_call+0x7e/0x83
 DWARF2 unwinder stuck at system_call+0x7e/0x83

plus four (or five) others. dhclient, ip, and a few gnome-applets. See the
messages file referenced above for the whole thing.

 ~ ~ ~ ~ ~ ~ ~

The second trace in that messages file I referenced includes:

 NetworkManage D ffff81002e0bf318     0  4837      1          4857  4813 (NOTLB)
  ffff81002b069be8 0000000000000046 0000000000000001 ffff81002e0bf140
  ffffffff80518520 00000000000075e7 0000000000000000 ffff81002e0bf140
  ffffffff80269f58 ffff81002e0bf140 ffff81002e80b3f0 ffff81002e80b3a0
 Call Trace:
  [__mutex_lock_slowpath+344/624] __mutex_lock_slowpath+0x158/0x270
  [mutex_lock+9/16] mutex_lock+0x9/0x10
  [_end+126837412/2126632680] :bcm43xx:bcm43xx_wx_get_rangeparams+0xec/0x2a0
  [ioctl_standard_call+623/944] ioctl_standard_call+0x26f/0x3b0
  [wireless_process_ioctl+260/976] wireless_process_ioctl+0x104/0x3d0
  [dev_ioctl+854/944] dev_ioctl+0x356/0x3b0
  [sock_ioctl+576/624] sock_ioctl+0x240/0x270
  [do_ioctl+49/160] do_ioctl+0x31/0xa0
  [vfs_ioctl+683/720] vfs_ioctl+0x2ab/0x2d0
  [sys_ioctl+106/160] sys_ioctl+0x6a/0xa0
  [system_call+126/131] system_call+0x7e/0x83
 DWARF2 unwinder stuck at system_call+0x7e/0x83

also in D state

 wpa_supplican D ffff810022248298     0  5953      1          6048  5887 (NOTLB)
  ffff810020077d28 0000000000000046 0000000000000000 ffff8100222480c0
  ffffffff80518520 00000000000055e7 0000000000000000 ffff8100222480c0
  ffffffff80269f58 ffff8100222480c0 ffffffff805505b0 ffffffff80550560
 Call Trace:
  [__mutex_lock_slowpath+344/624] __mutex_lock_slowpath+0x158/0x270
  [mutex_lock+9/16] mutex_lock+0x9/0x10
  [rtnl_lock+16/32] rtnl_lock+0x10/0x20
  [dev_ioctl+844/944] dev_ioctl+0x34c/0x3b0
  [sock_ioctl+576/624] sock_ioctl+0x240/0x270
  [do_ioctl+49/160] do_ioctl+0x31/0xa0
  [vfs_ioctl+683/720] vfs_ioctl+0x2ab/0x2d0
  [sys_ioctl+106/160] sys_ioctl+0x6a/0xa0
  [system_call+126/131] system_call+0x7e/0x83
 DWARF2 unwinder stuck at system_call+0x7e/0x83

 events/0      D ffff810037fbf2d8     0     4      1             5     3 (L-TLB)
  ffff810037f21ca0 0000000000000046 0000000000000000 ffff810037fbf100
  ffff8100222480c0 0000000000a43207 ffff81002e80b328 ffff81002e80b648
  ffff810037f21c80 ffffffff802a468b ffff81002edd5ae0 ffff81002edd5ae0
 Call Trace:
  [wait_for_completion+160/240] wait_for_completion+0xa0/0xf0
  [_end+126326789/2126632680]
:ieee80211softmac:ieee80211softmac_wait_for_scan_implementation+0x7d/0x90
  [_end+126326445/2126632680]
:ieee80211softmac:ieee80211softmac_wait_for_scan+0x45/0x50
  [_end+126324953/2126632680]
:ieee80211softmac:ieee80211softmac_clear_pending_work+0x21/0x210
  [_end+126326216/2126632680] :ieee80211softmac:ieee80211softmac_stop+0x10/0x20
  [_end+126779961/2126632680] :bcm43xx:bcm43xx_select_wireless_core+0xa1/0x470
  [_end+126781010/2126632680] :bcm43xx:bcm43xx_chip_reset+0x4a/0x90
  [run_workqueue+205/288] run_workqueue+0xcd/0x120
  [worker_thread+283/352] worker_thread+0x11b/0x160
  [kthread+211/272] kthread+0xd3/0x110
  [child_rip+10/18] child_rip+0xa/0x12
 DWARF2 unwinder stuck at child_rip+0xa/0x12

> I looked at the above WX calls into bcm43xx to see which of them might
> be causing a deadlock. Most
> are innocuous; however, the SIWSCAN could cause a problem as softmac
> calls back into bcm43xx to set the channel, and to send a management
> frame. If bcm->mutex were held because of a call by wpa_supplicant when
> NM triggers a scan, I think the deadlock could occur. In the patch
> below, I created wrapper functions for the calls to
> ieee80211softmac_wx_trigger_scan and
> ieee80211softmac_wx_get_scan_results. In the wrappers, I use
> mutex_trylock to return an error for
> any calls where there is mutex contention. If none, I release the mutex
> before calling softmac.
> 
> For completeness, I changed the mutex_lock to a mutex_trylock for all
> the WX routines.
> 
> I admit ignorance regarding locking. Is this a reasonable way to
> approach the problem? The patch
> doesn't break my system, but I never had the problem.

Logging a message when the driver is compiled with debugged would be useful.

But for the bigger picture, does this give you any ideas as to how I can try
to reproduce this more reliably? Parallel iwconfig eth1 in multiple terminals
doesn't seem to be giving the code any grief, even though it hits all the
ioctls. events/0 is doing a scan each time, can that be forced from userspace?

Ray
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